You can void a customer credit memo if the memo is related to an existing invoice (that is, if it was entered in the Credit Memos window. If it was applied instead to a receipt (that is, if it was entered in the Receive Money task window), you will first have to delete the receipt before you can void the related credit memo.
To void a selected credit memo in the Credit Memos window, click the Void button in the toolbar.
Then the Void Existing Invoice window appears. At The following credit memo will be voided as of, Sage 50 offers the system date as the default void date. Accept this date, or enter a new one. Then, to void the credit memo, click OK.
Note: In cases where maintaining an audit trail is not important, you can choose to delete rather than void a credit memo. When should I delete instead of voiding a credit memo?