You have a couple of choices here and you can select the option that best works for you.
1. you can VOID the CREDIT Memo - by going to Void Historical Documents - Purchase >> Transactions >> Void Historical and entering the necessary documents. This is the clearest way to correct. As you remove the data from the AP and GL in the same way it went into the modules. Of course you then need to re-enter and apply the correctly distributed Credit memos.
2. you can create correcting Journal Entries only in the GL. The challenge with this is that while quick and easy, it will be the least linked solution. The transaction in AP will be 'wrong' but the dollars in the GL will all balance. The AP to GL balance will be corrected, but you will have a hard time proving the data
I think these are the two options, now you can select, but I think best is #1 as it is the most correct way to enter and record correctly what happened.
