Good afternoon, @agreer.

For QuickBooks Desktop the best option would be is to remove the credit memo due to it not being paid and create a journal entry once the funds have been received from the collections agency to resolve the balance. 

For further advice I would reach out to your accountant.

Here's how to create a journal entry: Create a journal entry in QuickBooks Desktop.

If you have any other questions about recording the transactions or anything else QuickBooks related, we're always here to help. Have a great day!