seat mounting question '91 900

I just put my Recaro seat into my new? '91 and one of the mounting
holes stripped out. It is a ~1" square plate with an M10-1.5 that
seems to sit under the floor, but I don't think can be accessed from
under the car. Before I go tearing up the carpet and everything, can
anyone describe how to access it? Should I look at re-tapping the hole
and using a larger screw?
Thanks,
Robobass