To log a refund (that you've provided outside of WholeCell) for your customer for returned RMA devices, go to the 'RMAs' page on the left side of WholeCell, then click on the RMA ID in question.
On the RMA page, click on the green '$' button.
Here you can enter the refund details and any notes for this external transaction. Hit 'Save' when done.
Check out the 'Refund History' details on this page to see what you just entered.