My phone does not support my sim in my region (Nigeria)

What is the exact message you are seeing? If it is "SIM Not Supported" the phone is locked to a carrier. You need to contact that carrier and ask about their unlocking policy. You can contact Apple Support at the top of this page and they should be able to tell you who the carrier is.

Where did you buy the phone?

That message usually means the phone is locked to a carrier and you need to contact that carrier to get it unlocked.

~Lyssa