Chevrolet 2005 Express Van Owner's Manual page 64

5. Pull the rest of the lap belt all the way out of the
retractor to set the lock.
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6. To tighten the belt, pull the shoulder portion of the
belt to tighten the lap portion of the belt and feed
the shoulder belt back into the retractor. You
may find it helpful to use your knee to push down
on the child restraint as you tighten the belt.
7. Push and pull the child restraint in different
directions to be sure it is secure.
To remove the child restraint, just unbuckle the vehicle's
safety belt and let it go back all the way. The safety
belt will move freely again and be ready to work for an
adult or larger child passenger.