Aşağıdaki kodda ilkinde 5 ikincisinde 3 seçili olması
JSFIDDLE

<select id="a">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<select id="a">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script>
$("#a:eq(0) option[value='5']").prop('selected', true);
$("#a:eq(1) option[value='3']").prop('selected', true);
</script>

id="a" yerıne class a kullanınca düzeldi teşekkürler...