JSFiddle - React, Tailwind, and code Playground

HTML

<select id="sel" onchange='alert("changed: " + this.value)'>
  <option value='1' selected>One</option>
  <option value='2'>Two</option>
  <option value='3'>Three</option>
</select>
<input type="button" onclick='document.getElementById("sel").options[1].selected = true;' value="Change option to 2" />

JavaScript

var selEl = document.getElementById("sel");

selEl.options[1].selected = true;
selEl.onchange();