Negative Overdue Amount - Customer Card

Hello! My customer card shows a negative Overdue Amount in their statistics area on right hand side.

The negative balance is from a check that was applied to an invoice and the customer overpaid. This applied a "credit" or "negative balance" to their account.

After speaking with the client it needs applied to another invoice.


Is there a way to do this?


Any help would be greatly appreciated as I am a fairly new user to this system.