Buick 2009 Enclave Owner's Manual page 29

There is one guide for each outboard passenger
position in the rear seat. Here is how to install a comfort
guide to the safety belt:
1. Pull the elastic cord out from between the edge of
the seatback and the interior body to remove the
guide from its storage clip.
2. Place the guide over the belt and insert the two
edges of the belt into the slots of the guide.
1-25