GMC 1995 Safari Owner's Manual page 45

5. To tighten the belt, pull up on the shoulder belt while you push down
6. Push and pull the child restraint in different directions to be sure it is
on the child restraint.
secure.
To remove the child restraint, just unbuckle the vehicle's safety belt and let
it go back all the way. The safety belt will move freely again and be ready to
work for an adult or larger child passenger.
Securing a Child Restraint in a Center Seat Position
(Bench Seat)
You'll be using the lap belt.
See the earlier part about the top strap if the child restraint has one.