GMC Yukon Owner's Manual page 56

6. To tighten the belt, feed the shoulder belt
back into the retractor while you push down
on the child restraint.
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.
You'll be using the lap belt.
See the earlier part about the top strap if the child
restraint has one.
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