JSFiddle - React, Tailwind, and code Playground

HTML

<div class="class_for_all_multi_selects">
  <select multiple="multiple" name="1">
    <option value="1" selected='true'>option1</option>
    <option value="2" selected='true'>option2</option>
  </select>
</div>

<button id="uncheck" >Uncheck</button>

JavaScript

$('#uncheck').click(function(){

    $("div.class_for_all_multi_selects option:selected").prop('selected',false);    
});