You should do a search regarding replacement of the seat springs or swapping of the seat springs there is much info!
Basically you remove the seat from the car, then remove the "Seat Box", the seat bottom spring arrangment, then you can remove the seatcovering and padding, then you will have access to the springs themselves. You might be able to find a replacement spring somewhere, boneyard or maybe an upolstery shop, or maybe you can secure the protruding spring to another spring and therebye keep it inside the seat.
You might consider buying a new seat box $125 or getting one from your local boneyard ( I got mine for $20). Passenger side seats are usually in better shape! Good Luck.
here's a link:
4 hour seat swap, armrest ?