When a conversion is approved, the commission for that conversion is immediately forwarded to the Payments Page.
If you'd like to modify a commission, you can go back to the conversion where the commission originated, and do one of two things:
Disapprove the commission entirely - this will remove the commission from the balances page.
Modify the commission amount - you can open the right-side details panel click on the commission amount to edit this field.
Have you already paid out the commission?
If you have already settled the balance with an affiliate, and a refund takes place after the payment has been made, it will affect your affiliate's balance. You can read more about how balances are impacted by commission changes in this article.