In order to correct this error, open the invoice to which you applied the credit and follow these steps.
1.Click the History button at the top of the transaction window to display the list of all transactions linked to this invoice.
2.Click the listing for the credit you want to change, and click "Go To", to open the original credit transaction.
3.Change the customer name to another customer. (It doesn't matter which customer you choose because you're going to change it back.)
4.Click "Yes" in any warning dialogs QuickBooks displays about the results of making this change. Now you've destroyed the link between the credit and the invoice to which it was originally applied. (QuickBooks returns you to the original invoice window, where the credit no longer appears in the History dialog.)
5.Open the credit transaction you just moved to another customer.
6.In the Create Credit Memos transaction window, change the customer name back to the original customer name.
7.When you save the transaction, QuickBooks offers the original choices for applying this credit. Choose the correct invoice.