Recording a transaction for a customer refund

[Ursula]

Hello,

We had to refund a customer as there was a wrong part ordered.  The invoice was created and paid for.  We now have to do a refund for him but there is no refund button.  Can we use the credit so it will reverse the whole transaction within Express Accounts Accounting Software or is there an actual "Refund" button that we can use.  This is the first time we have had to do a refund after the invoice was already paid.  

Thanks