GMC 2010 Sierra - Manual (Page 101)

If more than one child restraint needs to be installed in
the rear seat, be sure to read Where to Put the
Restraint on page 2‑47.
1. Put the child restraint on the seat.
2. 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.
For crew cab second row seatings positions, tilt the
latch plate to adjust the belt if needed.
3. 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.
2-59