<h4>Cambio de valores en Select </h4>
<button type="button" onclick="Select_orden('1')" name="button">ordenar Select 1</button>
<button type="button" onclick="Select_orden('2')" name="button">ordenar Select 2</button>

<select  name="datos_select" id="datos_select" >
  <option value="1">Valor 1</option>
  <option value="2">Valor 2</option>
</select>
<script>
function Select_orden(valor){
document.getElementById('datos_select').value=valor;
}
</script>

('datos_select')

value=valor