Test Fiddle

HTML

<body>

  <div class="cmicrophone" id="cmicrophone">Currently:
    <select id="cmicrophone" class="cmicrophone select1" name="cmicrophone" onchange="">
      <option value="">Select Option</option>
      <option value="'S microphone is currently on. Please remind them to turn it ">OFF</option>
      <option value="'S microphone is currently off. Please remind them to turn it ">ON</option>
    </select>
  </div>
  <div class="microphone" id="microphone">Microphone:
    <select id="microphone" class="microphone select2" name="microphone">
      <option value=" " selected="selected">Select Option</option>
      <option value="ON. Thank you.">ON</option>
      <option value="OFF. Thank you.">OFF</option>
    </select>
  </div>

JavaScript

const cmicrophone = document.querySelector('.select1');
const microphone = document.querySelector('.select2');

function inputHandler(thisSelect, otherSelect) {
  // console.log(thisSelect.selectedIndex)
  if (thisSelect.selectedIndex == 1) {
    otherSelect.selectedIndex = 1;
  } else if (thisSelect.selectedIndex == 2) {
    otherSelect.selectedIndex = 2;
  } else {
    thisSelect.selectedIndex = 0;
    otherSelect.selectedIndex = 0;
  }
}

cmicrophone.addEventListener('input', event => {
  inputHandler(cmicrophone, microphone);
});

microphone.addEventListener('input', event => {
  inputHandler(microphone, cmicrophone);
});