How do you move the seat in a 93 mark VIII if the switches dont work?

I would suggest perhaps removing the seat and inspecting the wiring and plugs that operate the seat. Maybe a wire has come off or worn through over time from constant seat movement (like when you flip the seat back to get into rear seat)perhaps a plug has come off or has a loose connection. If that doesn't seem to do it go on E-bay (or an auto wrecker) and try and get yourself a cheap replacement seat switch. As with everything....time and patience...and a lot of swearing in the meantime!