You can issue a refund using the "Issue Refund" function in the control panel.

Note: You may be required to enter a manager override password.

On the Issue Refund screen, you'll see the following options

Type: Payment method of the transaction being refunded. Cash, Credit, Check, and Gift Card are the options.

Tax Rate 1(2,3): Tax rate for the refund

Reason: The reason for the reason.

Amount: This is where you enter the amount of the refund. 

Issue Refund: This will process the refund

Close: This will return you to the control panel.