If your payment split is for a pledge and you need to edit the payment to reflect this you can select the option Assign Pledge to Split. Alternatively if the payment is erroneously assigned to a pledge you can use the option Unassign Pledge from Split.
Select the Pledge you want to assign this payment to. If there is only one pledge then it will be automatically assigned to that pledge.
The payment has now been assigned and the details of the pledge should now be visible in the sublist. Use View Details in the options menu or double click on the split to view the pledge or other form (such as Order, Membership, Sponsorship, etc).
To unassign the pledge just select Unassign Pledge from Split and the payment will revert to a donation.