On the affiliate's Checkouts tab tick the commissions, choose Mark as Unpaid or Mark as Rejected in the dropdown, click Update and confirm. The status changes immediately and a success message is shown.

Status rules: an Unpaid commission can become Paid, Paying (a system-only state) or Rejected; a Rejected one can be moved back to Unpaid or Paid from this screen; a Paid commission cannot be changed here (reverse it by handling the payout outside Sprwt). Commissions the system has marked Total Refund or Partial Refund cannot be changed manually. Selected commissions that are not allowed to move are silently skipped; if none of them can move you see "Cant update selected comissions!".