<a id='btn1' onclick='selectCity(event)'>Moscow</a>
<a id='btn2' onclick='selectCity(event)'>Tokyo</a>

<select id='mySelect'>
  <option value='0'>Moscow</option>
  <option value='1'>Tokyo</option>
</select>

<script>
function selectCity(e) {
if(e.target.id === 'btn1')
  document.getElementById('mySelect').selectedIndex = '0';
else
if(e.target.id === 'btn2')
  document.getElementById('mySelect').selectedIndex = '1';
}
</script>