How to reduce prepayment amount in Payables

Hello

We are facing one scenario in which we want to reduce prepayment amount.

Example -  we have done a prepayment of $1000 and later on we have returned some defective products worth $200, as we have already done a prepayment.... how we can balance the entries assuming we will get $200 in cash from the vendor.

we are on oracle 11.5.10.2

Thanks