GMC Sierra Denali 2006 Owner's Manual page 31

To unlatch the belt, push the button on the buckle.
Rear Safety Belt Comfort Guides
Rear seat comfort guides may provide added safety belt
comfort for older children who have outgrown booster
seats and for some adults. When installed on a shoulder
belt, the comfort guide positions the belt away from
the neck and head.
There is one guide for each outside passenger in the
rear seat. Here is how to install a comfort guide and use
the safety belt:
1. Remove the guide from its storage clip on the
interior body.
2. Place the guide over the belt and insert the
two edges of the belt into the slots of the guide.
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