GMC Sierra Classic 2007 Owner's Manual page 16

To return the seatback to an upright position, do
the following:
1. Lift the lever fully without applying pressure to
the seatback and the seatback will return to
the upright position.
2. Push and pull on the seatback to make sure it
is locked.
16
Power Reclining Seatbacks
If your seats have power reclining seatbacks, use
the vertical power seat control located on the
outboard side of the seat(s).
•
To recline the seatback, press the control
toward the rear of the vehicle.
•
To raise the seatback, press the control
toward the front of the vehicle.