Button to zero out a record

I have an app where payments are applied to loans.

All is working as expected.

On occasion, a loan needs to be written off/zero'd out.

How can I create a button that will change a records value to 0? I realize that I could just put in a payment with the payoff amount, but that would record as a payment being made. I need a way to zero out the remaining amount due without showing it as being a payment.