GMC Sierra Denali Classic 2007 Owner's Manual page 59

4. Pull the rest of the shoulder belt all the way 5. To tighten the belt, push down on the child
out of the retractor to set the lock. restraint, pull the shoulder portion of the belt
to tighten the lap portion of the belt and
feed the shoulder belt back into the retractor.
If you are using a forward-facing child
restraint, you may find it helpful to use your
knee to push down on the child restraint
as you tighten the belt.
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