GMC 2008 Envoy Denali Owner's Manual page 31

4. To make the lap part tight, pull up on the
shoulder belt.
It may be necessary to pull stitching on the safety
belt through the latch plate to fully tighten the
lap belt on smaller occupants.
To unlatch the belt, push the button on the buckle.
The belt should go back out of the way.
Before you close a door, be sure the belt is out of the
way. If you slam the door on it, you can damage
both the belt and your vehicle.
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