How to enter this credit

SOLVED

I had entered a purchase invoice twice and I had not realised it. And consequantly, I paid this purchase invoice twice but luckily, my supplier found this and gave me a credit for this invoice and told me that I could pay less in the next payment. How to enter this credit and how to deal with this credit in system? The most importance is when I paid this invoice, I paid it together with many invoices in a big total amount in the same check. That is why I do not know how to do next.

Thank you very much!