GMC Yukon XL 2015 Owner's Manual page 128

3. Pick up the latch plate, and run
the lap and shoulder portions of
the vehicle's safety belt through
or around the restraint. The child
restraint instructions will show
you how.
Tilt the latch plate to adjust the
belt, if needed.
4. Push the latch plate into the
buckle until it clicks.
Position the release button on
the buckle so that the safety belt
could be quickly unbuckled if
necessary.
Seats and Restraints
5. Pull the shoulder belt all the way
out of the retractor to set the
lock. When the retractor lock is
set, the belt can be tightened but
not pulled out of the retractor.
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