Unhook your battery first. Start unbolting any bolts you see around the steering column. Take the plastic "cowl" from around the steering wheel off. Once that's done, hmmm...Idunno. Just look around and see if you see a yellow sensor or wire. That's your airbag. Unhook it if it clips-it should. From what I remember, the top of the airbag cover just pops off, but it's been a while since I've done this. The airbag components are inside the cover, I think that's when you'll see the yellow wire. From there, if you can get the cover off, just replace it. If all this fails, definitely either go to a shop that has rebuilt a celica before (first bet) and if you can't find one, go to a Toyota dealership.