Employee expense return

Dear,

Our scenario like that : we paid a petty cash to employee like 1000 USD and later on employee submit the invoices 800 USD and 200 USD employee has to return. Please let me know how I can proceed this transaction.

I know we can record first prepayment and paid to employee 1000 USD and later when user submit the invoice then we enter the expense report and apply with the prepayment but I want to know the remaining amount how I can adjust with prepayment which is return as cash .

Thanks