Combo-box value is not updating to the initial value

Hello All,

we are using a combo-box in a request pop-up button.

So user has given the details to all the fields in the pop-up and decided to cancel the pop-up window.

Again he wants to re-request and clicked on request button, now the combo-box value did not set to initial value or empty value.

It was showing the previous selected value.

How to set to initial or blank value to that.