Javascript to clear a populated field

Hello all!

I am looking for help   I have a form where I have two dropdowns.  When you choose an item from the first drop down it populates the list for the 2nd dropdown.  Problem is when the user decides to change their mind on the first dropdown and the 2nd drop down is already populated the new list appears but the field within the dropdown doesn't clear for the user to make a new choice.  How can I get the field to clear?

Here is the script I am using

Thanks!!!

Jodi