Hummer 2006 H3 Owner's Manual page 116

2. Remove the end cap.
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3. Pull the lever labeled "PULL" from left to right to
loosen the crossrail.
4. Repeat Steps 1 through 3 to the opposite end of
the crossrail.
5. Once both sides of the crossrail are loose, adjust
the crossrail to the desired position.
6. Push the lever labeled "PULL" from right to left to
lock the crossrail in place.
7. Reinstall end cap and lock by turning the
key clockwise.
8. Repeat Steps 5 through 7 to the opposite end of
the crossrail.