Hummer 2006 H2 Owner's Manual page 16

To return the seatback to an upright position, do the
following:
1. Pull the lever labeled 3 toward you.
2. While still holding lever 3 toward you, grasp the top
of the seat and pull it toward you slightly.
1-10
3. Let go of lever 3 and pull the seat completely down.
4. Push down on the seat firmly. Try pulling it up to
be sure it is locked into place.
5. Pull up on the release
lever labeled 1 and
then pull up on
the seatback until the
seatback locks into
the upright position.