Returns after Rebate Settlement

Dear Experts

Please adivce how to proceed with the following scenario raised in our company.

1. I have entered rebate agreement with a customer for a year

2. Based on the performance in the 1st quarter, I have done the settlement & issued credit for him

3. In the second quarter he is not eligible for issuing the rebate

4. At the same time, there is a return from him from the issues of 1st quarter.

Please let me know how the system will react for the returns after rebate settlement.

Thanks

Jey