I have a 1999 Chevy blazer and I’ve read on here that the handle breaking off has been a common issue among blazers and that’s what happened to me before I bought my car from my dad. The handle just became loose and wouldn’t actually move the seat back but would just spin around. He ended up put a pair of pliers on the screw (I believe? It’s hard to tell because it’s covering) that controls the seat back but the handle is still loosely attached. Is there any way to fix this myself? I’d like to if I could and I still have the handle.

 

I think the common issue is the plastic handle you see when you open the door / it is shaped like a comma/ is what breaks. What you are describing in your post is the splined metal shaft is spinning. Look to see if the plastic interface to that splined shaft is striped or is it the metal shaft splines are gone. I think you just need a new handle to solve the problem. That is if the vise grips haven't destroyed the splines. Go to a salvage yard and search for a good handle. You have to be lucky because this is a common problem and many of the new vehicles in the salvage yard will also have the defective handles.
I seem to remember some one made a metal replacement for the plastic handle. It was not cheap and I do not remember who offered this replacement. You might do a search on E Bay and if you do find one, please post the info on the forum for others. Thanks, JIm

 

Here is an adapter kit I used on mine that has held up for several years. It comes with the handle and adapter that goes onto the existing shaft. Hopefully the pliers haven't messed up the metal piece the handle was attached to. Kit is $19.95
Seat Recline Repair Kit