2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 102

4. Pull the rest of the shoulder belt all the way out of the retractor to set the lock. 5. To tighten the belt, push down on the child restraint, pull the shoulder portion of the belt to tighten the lap portion of the belt and feed the shoulder belt back into the retractor. When installing a forward-facing child restraint, it may be helpful to use your knee to push down on the child restraint as you tighten the belt. 2-60