GMC Sierra 2018 Owner's Manual page 71

70 Seats and Restraints
If the webbing locks in the latch
plate before it reaches the
buckle, tilt the latch plate flat to
unlock.
3. Push the latch plate into the
buckle until it clicks.
Pull up on the latch plate to
make sure it is secure. If the
belt is not long enough, see
Seat Belt Extender 0 73.
Position the release button on
the buckle so that the seat belt
could be quickly unbuckled if
necessary.
4. If equipped with a shoulder belt
height adjuster, move it to the
height that is right for you. See
Shoulder Belt Height Adjuster
later in this section for
instructions on use and
important safety information.
5. To make the lap part tight, pull
up on the shoulder belt.