Chevrolet VENTURE 2001 Manual page 70

When you sit in the center position of the bench seat,
you have a lap safety belt, which has no retractor.
To make the belt longer, tilt the latch plate and pull
it along the belt.
1-58
To make the belt shorter, pull its free end as shown until
the belt is snug.
Buckle, position and release it the same way as the lap
-
part of a lap shoulder belt. If the belt isn't long enough,
see "Safety Belt Extender" at the end of this section.
Make sure the release button on the buckle is positioned
so you would be able to unbuckle the safety belt quickly
if you ever had to.