javascript - GetElementById how to get value of tabindex C# -

i'm trying choose 1 of country code in webbrowser windows form geting id code: webbrowser1.document.getelementbyid("ulcountrymenu_alt").setattribute("value", "uk"); it's not changing in webbrowser, or should use getelementbytagname?

 <div id="ulcountrymenu_alt">                <ul class="scroll-widget-scrollable scroll-widget-ulcountrymenu">             <li tabindex="109" data-attr-val="+93" data-attr-country-code="af"><a href="#" aria-label="afghanistacn"><span class="famfamfam-flag-af"></span>&nbsp;afghanistan (+93)</a></li><li tabindex="109" data-attr-val="+355" data-attr-country-code="al"><a href="#" aria-label="albania"><span class="famfamfam-flag-al"></span>&nbsp;albania (+355)</a></li><li tabindex="109" data-attr-val="+213" data-attr-country-code="dz"><a href="#" aria-label="algeria"><span class="famfamfam-flag-dz"></span>&nbsp;algeria (+213)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="as"><a href="#" aria-label="american samoa"><span class="famfamfam-flag-as"></span>&nbsp;american samoa (+1)</a></li><li tabindex="109" data-attr-val="+376" data-attr-country-code="ad"><a href="#" aria-label="andorra"><span class="famfamfam-flag-ad"></span>&nbsp;andorra (+376)</a></li><li tabindex="109" data-attr-val="+244" data-attr-country-code="ao"><a href="#" aria-label="angola"><span class="famfamfam-flag-ao"></span>&nbsp;angola (+244)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="ai"><a href="#" aria-label="anguilla"><span class="famfamfam-flag-ai"></span>&nbsp;anguilla (+1)</a></li><li tabindex="109" data-attr-val="+672" data-attr-country-code="aq"><a href="#" aria-label="antarctica"><span class="famfamfam-flag-aq"></span>&nbsp;antarctica (+672)</a></li><li tabindex="109" data-attr-val="+1268" data-attr-country-code="ag"><a href="#" aria-label="antigua, barbuda"><span class="famfamfam-flag-ag"></span>&nbsp;antigua, barbuda (+1268)</a></li><li tabindex="109" data-attr-val="+54" data-attr-country-code="ar"><a href="#" aria-label="argentina"><span class="famfamfam-flag-ar"></span>&nbsp;argentina (+54)</a></li><li tabindex="109" data-attr-val="+374" data-attr-country-code="am"><a href="#" aria-label="armenia"><span class="famfamfam-flag-am"></span>&nbsp;armenia (+374)</a></li><li tabindex="109" data-attr-val="+297" data-attr-country-code="aw"><a href="#" aria-label="aruba"><span class="famfamfam-flag-aw"></span>&nbsp;aruba (+297)</a></li><li tabindex="109" data-attr-val="+247" data-attr-country-code="ac"><a href="#" aria-label="ascension"><span class="famfamfam-flag-ac"></span>&nbsp;ascension (+247)</a></li><li tabindex="109" data-attr-val="+61" data-attr-country-code="au"><a href="#" aria-label="australia"><span class="famfamfam-flag-au"></span>&nbsp;australia (+61)</a></li><li tabindex="109" data-attr-val="+43" data-attr-country-code="at"><a href="#" aria-label="austria"><span class="famfamfam-flag-at"></span>&nbsp;austria (+43)</a></li><li tabindex="109" data-attr-val="+994" data-attr-country-code="az"><a href="#" aria-label="azerbaidijan"><span class="famfamfam-flag-az"></span>&nbsp;azerbaidijan (+994)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="bs"><a href="#" aria-label="bahamas"><span class="famfamfam-flag-bs"></span>&nbsp;bahamas (+1)</a></li><li tabindex="109" data-attr-val="+973" data-attr-country-code="bh"><a href="#" aria-label="bahrain"><span class="famfamfam-flag-bh"></span>&nbsp;bahrain (+973)</a></li><li tabindex="109" data-attr-val="+880" data-attr-country-code="bd"><a href="#" aria-label="bangladesh"><span class="famfamfam-flag-bd"></span>&nbsp;bangladesh (+880)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="bb"><a href="#" aria-label="barbados"><span class="famfamfam-flag-bb"></span>&nbsp;barbados (+1)</a></li><li tabindex="109" data-attr-val="+375" data-attr-country-code="by"><a href="#" aria-label="belarus"><span class="famfamfam-flag-by"></span>&nbsp;belarus (+375)</a></li><li tabindex="109" data-attr-val="+32" data-attr-country-code="be"><a href="#" aria-label="belgium"><span class="famfamfam-flag-be"></span>&nbsp;belgium (+32)</a></li><li tabindex="109" data-attr-val="+501" data-attr-country-code="bz"><a href="#" aria-label="belize"><span class="famfamfam-flag-bz"></span>&nbsp;belize (+501)</a></li><li tabindex="109" data-attr-val="+229" data-attr-country-code="bj"><a href="#" aria-label="benin"><span class="famfamfam-flag-bj"></span>&nbsp;benin (+229)</a></li><li tabindex="109" data-attr-val="+1441" data-attr-country-code="bm"><a href="#" aria-label="bermuda"><span class="famfamfam-flag-bm"></span>&nbsp;bermuda (+1441)</a></li><li tabindex="109" data-attr-val="+975" data-attr-country-code="bt"><a href="#" aria-label="bhutan"><span class="famfamfam-flag-bt"></span>&nbsp;bhutan (+975)</a></li><li tabindex="109" data-attr-val="+591" data-attr-country-code="bo"><a href="#" aria-label="bolivia"><span class="famfamfam-flag-bo"></span>&nbsp;bolivia (+591)</a></li><li tabindex="109" data-attr-val="+387" data-attr-country-code="ba"><a href="#" aria-label="bosnia & herzegovina"><span class="famfamfam-flag-ba"></span>&nbsp;bosnia & herzegovina (+387)</a></li><li tabindex="109" data-attr-val="+267" data-attr-country-code="bw"><a href="#" aria-label="botswana"><span class="famfamfam-flag-bw"></span>&nbsp;botswana (+267)</a></li><li tabindex="109" data-attr-val="+55" data-attr-country-code="br"><a href="#" aria-label="brazil"><span class="famfamfam-flag-br"></span>&nbsp;brazil (+55)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="vg"><a href="#" aria-label="british virgin islands"><span class="famfamfam-flag-vg"></span>&nbsp;british virgin islands (+1)</a></li><li tabindex="109" data-attr-val="+673" data-attr-country-code="bn"><a href="#" aria-label="brunei darussalam"><span class="famfamfam-flag-bn"></span>&nbsp;brunei darussalam (+673)</a></li><li tabindex="109" data-attr-val="+359" data-attr-country-code="bg"><a href="#" aria-label="bulgaria"><span class="famfamfam-flag-bg"></span>&nbsp;bulgaria (+359)</a></li><li tabindex="109" data-attr-val="+226" data-attr-country-code="bf"><a href="#" aria-label="burkina faso"><span class="famfamfam-flag-bf"></span>&nbsp;burkina faso (+226)</a></li><li tabindex="109" data-attr-val="+257" data-attr-country-code="bi"><a href="#" aria-label="burundi"><span class="famfamfam-flag-bi"></span>&nbsp;burundi (+257)</a></li><li tabindex="109" data-attr-val="+855" data-attr-country-code="kh"><a href="#" aria-label="cambodia"><span class="famfamfam-flag-kh"></span>&nbsp;cambodia (+855)</a></li><li tabindex="109" data-attr-val="+237" data-attr-country-code="cm"><a href="#" aria-label="cameroon"><span class="famfamfam-flag-cm"></span>&nbsp;cameroon (+237)</a></li><li tabindex="109" data-attr-val="+1" data-attr-country-code="ca"><a href="#" aria-label="canada"><span class="famfamfam-flag-ca"></span>&nbsp;canada (+1)</a></li><li tabindex="109" data-attr-val="+238" data-attr-country-code="cv"><a href="#" aria-label="cape verde"><span class="famfamfam-flag-cv"></span>&nbsp;cape verde (+238)</a></li><li tabindex="109" data-attr-val="+1345" data-attr-country-code="ky"><a href="#" aria-label="cayman islands"><span class="famfamfam-flag-ky"></span>&nbsp;cayman islands (+1345)</a>