Good afternoon, @office105.
Thanks for reaching out to the Community.
At this time, QuickBooks Online doesn't offer a feature to apply a credit memo to a refund check.
For now, you can create a Receive Payment and apply the credit memo to that, and here's how:
- Select New option in the left corner.
- Choose Receive payment or Receive invoice payment.
- Complete these fields as follows, including (Customer, Date, Memo).
- Under Credits, click on Credit Memo, or Give credit.
- Verify that the total to pay (if any) is correct after applying the Credit Memo.
- Pick Save and Close.
For more detailed instructions, please refer back to this article: Enter and apply credit memos and delayed credits in QuickBooks Online.
If you have any more questions or concerns, please don't hesitate to comment below. Have a good one!