You can cancel a payment using the Dashboard only when its status is "uncaptured." If the payment status is different, you'll need to contact the creator directly to request a refund.
To cancel uncaptured payments using the Dashboard:
Find the payment you want to cancel on the Payments page.
Click the three buttons menu to the right of the payment, then select "Cancel payment".
Select a reason for cancelling, then click "Yes". If you select "Other", you must add a note explaining the reason for cancelling the payment.