How to apply payment to correct invoice

I created 2 invoices a year apart. I received 2 payments a year apart. Somehow the payments got applied to the wrong invoice. Don't know how it happened, since they were a year apart. The amounts are the same so I show a zero balance, however I want to correct the payment to the correct payment. i.e. Invoice 1 should have been paid by payment 1, Invoice 2 should have been paid by payment 2. 1 was paid by 2 and 2 was paid by 1. Any clue how I can straighten this out. Tx