Chevrolet MONTE CARLO 1998 Manual page 37

Positions
Lap-Shoulder Belt
The positions next to the windows have lap-shoulder
belts. Here's how to wear one properly.
1.
2.
Pick up the latch plate and pull the belt across you.
Don't let it get twisted.
The shoulder belt may lock if you pull the belt across
you very quickly. If this happens, let the belt go back
slightly to unlock it. Then pull the belt across you
more slowly.
Push the latch plate into the buckle until it clicks.
Pull up on the latch plate to make sure it is secure.