Chevrolet 1998 Express Van Owner's Manual page 17

6. Insert the red handled locking pin into the seat
base, lifting the seat slightly to line up the pin with
the base.
7.
8.
9.
10.
Rotate the red handle down until it is in
the
retaining clip.
Replace the carpet/mat flap to its original position.
Repeat this procedure for the other seat base.
Connect the quick release latch plates for the lap
shoulder belts by inserting the latch plates into the
buckles attached at the outboard positions of the
bench seat. Do not twist the belt.