OK. What have I done ow?
1997 F150 Lariat w/bucket seats.
I removed the armrest from my driver's captain's chair to re-upholster the seat back.
Now that I want to re-install, thee is nothing inside the seat back frame that is threaded to screw the attaching bolt into.
There is just a hole...........
What have I done NOW ??

how do I fix it?????

 

The big nut plate fell down into the seat back
You might be able to fish it up and into position again
You might have to pull some of the seat back upholstery off to gain access

 

OK
Found it...it was a bit farther forward.
All good now.....