Thank you for posting here on the Community page, @Beylee.

I'm here to guide you on how to record these transactions in QuickBooks Online (QBO).

First, you need to issue a check to your customer using the Accounts Receivable account for the overpayment amount. Then, create a payment and select the check recorded and the existing credits.

Here's how to enter the check:

1. Open your QBO account, then select Check from the New (+) icon.
2. Pick the customer's name under the Payee section.
3. Under Category select Accounts Receivable, then enter the overpaid amount.
4. Save the check.

Once completed, follow these steps to link the check and the unapplied amount.

1. Open your customer's transaction list.
2. Click on the drop-down arrow under New transaction and choose Payment. 
3. On the Receive Payment window, select the check under the Outstanding Transactions section and the Unapplied Payment under the Credits.
4. Hit Save and close.

You can also check this article for other tips on how to handle a customer credit or overpayment in QBO.

As always, feel free to open the topics from this link in case you need guides while working with QuickBooks in the future.

Mention my name in the comment section below if you have any other questions. I'm always here to help you out. Keep safe always!