In this article we can able to show how to change value in drop
down based on button click
In the SharePoint List Edit page having button and column
with name “Status” by default it was showing Status as Open, when we click on
the button it will change the value to completed.
<script>
function ChangeStatus(){
$('Select[title=Status]').val('Completed');
}
</script>
<table>
<tr>
<td ><input type="button"
id="btn" value="Change the Status"
onclick="ChangeStatus();"/></td>
</tr>
</table>