Offsetting Payment in an A/R account with the same amounts.

I had an Invoice and Credit in an Accounts Receivable (A/R) account for the same invoice with the same amount I wanted to offset them as a Payment. I used Transactions -> Customers -> Accept Customer Payments to select the Invoice and Credit and saved it. But I chose the incorrect Credit, which had the same amount, but was for a different Invoice. Now I have the Credit from the original Invoice still in the credits for that Accounts Receivable and I don't know the Invoice number of the Credit I selected on the offsetting Payment entry.