Simply begin in the new CHECK screen, rather than the PAY BILLS screen.  Select the Vendor you want to pay bills and credits for (separately, not auto-applied).   On the right side of the CHECK screen, all of your vendor's bills and credit memos will show up.  Select the first BILL you want to pay.   The screen CHANGES to Bill Payment!  Now you see a LIST of Bills and Credit Memos to select.   All the way down at the bottom, the Credits will be listed separately -  and can be applied to the payment as a whole, not  specifically towards any particular Bill.  Let me know if this helps!