How do i allocate a refund to a customer that was paid throught the bank in quickbooks online?

Welcome to the Community space, hanneliel-prit-c.

I'll give steps on how to record a refund.

When a customer asks for a refund for an item or service, you can use the refund receipts option.

Here's how: 

1. Go to + New > Refund receipt or Give refund.
2. Select the customer you want to refund from the Customer drop-down menu.
3. From the Refund From drop-down list, choose the bank account where you deposited the payment for the invoice to.
4. Add all products or services the customer returned in the Product/Service column.
5. Make sure to fill the date, quantity, rate, amount, tax, and other fields accordingly, then click Save and close.

For other ways of recording a refund to a customer, you can read this article: Record a customer refund in QuickBooks Online.

To help manage your customers, check out this guide: Add and manage customers in QuickBooks Online.

If you have any additional questions regarding the process or need help with other customer transactions, please let me know in the comments below. Have a good day ahead.