Sounds like this was not possible; trade had to be accepted as-is or rejected, can't modify past the trade deadline.
The only sort of tweaks that can be done are waiving aspects, like player physicals, or reducing compensation if there is cash or picks are involved. Cash cannot be increased and picks can't be added but they can be reduced or protection removed. Since those things are already in the trade that was approved it's not much of an issue to lessen them because they aren't the primary pieces that make it legal like salary matching.