you will probly have to take the seat out and fix it.
easy cheap not done right fix= put a bolt with a big washer through the floor from the bottom of the car and bolt the seat back doun and probly fix it again anyway in a few months.
Right way= pull seats out along with carpet and patch or even replace floor pan. Install new seat stud's and reinstall carpet and seats.<---- not as easy as I made it sound lol.