A credit card payment was refunded using a check. If I go into the original payment and do a refund, will it duplicate the payment back to the customer?

Hello, sheilaweigel17-g.

Happy to give details on how refunds work in QuickBooks Online. 

You don't have to go back to the original payment to do a refund. You would simply create a Refund receipt.

It's not really an adjusting entry but a regular transaction detailing the refund. Doing this won't create a live refund on the customer's credit card. Instead, it will simply record the event in your books. 

If you haven't recorded the refund in QuickBooks yet, here's how to do it: 

1. Click the + New icon, then select Refund receipt.
2. Select the customer under Customer.
3. Choose the bank account under Refund From.
4. Set the Payment method to Credit Card.
5. Enter the details of the refunded purchase. 
6. Add other important details such as message, the Refund receipt number, etc..
7. Once done, click Save and close. 

What happens when you create a refund receipt: It will simply decrease the bank's balance and return the item to your inventory (if your customer purchased it). 

Note: Using a check instead of the refund receipt might have incorrect calculations on your books. 

More details can be found here: Void or refund customer payments in QuickBooks Online.

If you have a QuickBooks Payments account, the refund process is different. This is done through the Merchant Services Center. Doing this will actually refund the customer's credit card. 

If you'd like to know more, you can check this article: Void or refund transactions in QuickBooks Payments.

Ready to reconcile your customer payments or your bank account as a whole? I'm sure you'll find this article helpful: Reconcile an account in QuickBooks Online.

I'd be more than happy to offer help again if you have questions handling customer payments. Do you have other concerns instead? Let me know and I'll assist you.