If you've found a mistake on a payment that has not been released yet, you'll need to reset the payment, make the changes and then submit it for approval again.
To Reset a Payment
1. Go into the details view of the payment.
2. Go to Actions on the top right corner and then Reset Payment. This will return the payment back to the In-progress tab in Reset status. You can then make the necessary changes and resubmit it for approval.
A payment cannot be reset once it's been released.