There are three ways to credit a grant payment.
1. You can make a negative payment against the installment for the full amount which will preserve the original amount awarded but it will also look like there is an unpaid balance.
You would want to include information in the payment comments regarding the return funds.
2. You can add a negative installment that will revert the grant amount to $0 but you would want to include installment conditions reflecting the return.
Here is what each scenario looks like:
3. Yet another option would be, if you wanted Board Members to have visibility of the returned grant money and it's explanation, enter a manual grant request as a solution to track the returned money. It could be entered into an "Internal" miscellaneous manual grant entry process