const selectForm = document.getElementById('assesment');

selectForm.addEventListener("change", function(){
  if(selectForm.value === '2022'){
     alert('2022 Code will run');
  }
  if(selectForm.value === '2021'){
    alert('2021 Code will run');
  }
  if(selectForm.value === '2020'){
    alert('2020 Code will run');
  }
   if(selectForm.value === '2019'){
    alert('2019 Code will run');
  }
  
});

<form>
  <select id="assesment" class="target">
      <option value="0">ASSESSMENT YEAR</option>
      <option value="2022">2022 Assessment</option>
      <option value="2021">2021 Assessment</option>
      <option value="2020">2020 Assessment</option>
      <option value="2019">2019 Assessment</option>
  </select>
</form>