JSFiddle - React, Tailwind, and code Playground

HTML

<select id="select1" >
  <option value="apple" selected>Яблоко</option>
  <option value="pear" >Груша</option>
</select>
<select id="select2">
  <option value="apple" >Яблоко</option>
  <option value="pear" selected>Груша</option>
</select>

JavaScript

var firstSelect = document.getElementById("select1"),
    secondSelect = document.getElementById("select2");

secondSelect.onchange = function(event) {
    if (this.value === "apple") {
        firstSelect.value = "pear";
    }
}