Use the wrecker controls to lower the tractor until there is ½ inch to ¾ inch of clearance between the 5th wheel and the trailer plate.
The remaining weight of the trailer will now be resting on the trailer legs.
Make sure the trailer is not standing too high on the trailer legs and that the trailer has separated completely from the tractor.
Lower the tractor to towing height and retract the under-reach by roughly one foot. This will release the tractor’s connection to the trailer’s king pin but still keep the tractor under the trailer.