How do you enter a vendor credit memo, or adjust a vendor invoice aleady entered?

Hi there, @RetiredLF.

Let me guide you on how to enter a credit memo in QuickBooks Desktop.

1. Go to the Banking menu, then tap Make Deposits.
2. If the Payments to Deposit window appears, click OK.
3. In the Make Deposits window, select the Received from the drop-down and choose the vendor who sent you the refund.
4. In the From Account drop-down, select the appropriate Accounts Payable account.
5. In the Amount column, enter the actual amount of the Vendor check.
6. (Optional) Enter a memo, check number, payment method, and class.
7. Hit Save & Close.

Then you have to record the refunded amount:

1. Click Enter Bills on the Home page.
2. Choose the name of the Vendor.
3. Enter the amount of the bill.
4. Choose either of the two tabs:
   1. Expense
   2. Items
5. Add the specific details of the bill.
6. Click Save and Close.

For additional reference, you can check this article: Record a vendor refund in QuickBooks Desktop.

On the other hand, you can also check this link for your future reference about QuickBooks Desktop: Help articles for QuickBooks Desktop.

Please let me know if there's anything you need when applying customer credits, please don't hesitate to leave a comment below. Keep safe always.