Hello there, @Quick Lab. 

Thanks for following this thread. I'm here to guide you on how to process a refund on your customer's credit card. 

If you're trying to record this in QuickBooks Online, you don't need to have your customer's credit card information. This process is for recording purposes only and we use a refund receipt to refund the customer's credit card. Here's how: 

1. Click the + New menu, then select Refund Receipt.
2. Select the name of the customer. 
3. From the Payment Method drop-down menu, select the type of credit card your customer uses (Visa, MasterCard, etc.).
4. Check the Process Credit Card box.
5. Go to the Product/Service column, then select the product/service item you use for refunds. You can click Add New to set up one if you don't have any yet. 
6. Enter the Amount (partial) as a positive number and all other information. 
7. Select Save.

Once done, you'll want to contact your customer and ask their details so you can send the refund manually.

However, if you subscribed to QuickBooks Payments, there is a different way of processing a refund to your customers. To learn more about it, please see this article for your guide: How to void or refund a credit card payment.

I'll be looking forward to answering your next post here in the Community. Take care.