You can apply this Overpayment Credit to subsequent invoices/bills in one of 2 ways:
1. Create a New Payment for $0
You can create a New Payment, and set the amount to $0. When you get to the allocation screen, select the Overpayment Credit, and find another bill you wish to apply it to. Type in the credit amount in the allocation box on the bill line and hit Save and Confirm.
2. As part of another Payment
When applying another payment for the same supplier/customer, simply follow the above process to select an Overpayment Credit and apply to another bill.