Buy a repair manual for the Toyota Previa. Look up the pages that tell how to change the supercharger. Read those pages. Take the old supercharger out. Buy a new one and put the new one in. Drive car away.
I assume you are speaking about a turbocharger, here, so anyway, it is a pretty involved job because it requires disconnecting or cutting the exhaust pipe off. once out of the way, you may also need to remove parts of the intake, or the engine covers to gain access. You should also drain the oil and engine coolant before.
You have to Drain the old oil out, replace the oil filter, add new oil, check level and top up as necessary. Is very important that you check level, because if is more the level that you need, this can be problem for you
If you have a supercharger on that kind of vehicle, then I would say to do whatever you did before, because only a loon would have a supercharger on that.
I hate to say it but if you are asking this question you probably don't have the know how to perform this job. i know it is really expensive but this is one thing you dont want to screw up.