You can issue a refund in Teesom from the Customer Account screen. The process differs slightly depending on whether the payment was made through an Integrated Gateway or manually entered.
Regardless of the payment type, the first step is to unapply the payment on the Customer Account screen.
To access a customer’s account, open the Main Menu and select "Customers." On the "Customers" screen, search for the customer and click their name to open their account page.