Prepayment Question

An employee received a temporary advance for travel expense with the Invoice type of Prepayment.  The actual costs were less than the advance so the employee has paid the difference back to the company.  If I do a misc. receipt to debit cash and credit the prepayment account, how can I update the AP Prepayment Invoice to show as no longer open?  The system does not allow me to update the Prepayment Type from Termporary to Permanent.  This invoice is in our France OU so is AX Payables.

Thanks,

Brenda