Are you asking about the seat or the back?

 

the seat bottom
I put it up to get to jack and now the seat will not fold back down

 

I believe that truck is like my 15 and the rear seat bottom folds up, not the back folding down. Believe it’s been that way since the LMM trucks. Classic body trucks did fold down flat but not the newer trucks

 

the seat bottom
I put it up to get to jack and now the seat will not fold back down

 

Try giving it a good, solid, fast hit with the palm of your hand on the outside edge of the seat? That’s the way the newer ones are, not sure if your style has a release latch or something.

 

Perhaps something fell into the hinge area preventing it from folding back down.

 

I had something behind the seat.. when seat lifted it fell down and jammed..