Note! To be able to refund internet payments your role need the "Finance - List internet payments" and "Finance - Refund internet payments" right.
Go to Back Office > Finance > Internet payments
Find the purchase you want to refund. You can search by receipt, transaction or order number, the person who purchased or the date it was purchased.
Check the purchase and press "Refund". The same payment method that was used to pay for the purchase will be used when refunding.