I upgraded my iPad Air to a new iPad Pro but none of my previously purchased music was transferred

I upgraded my iPad Air to a new iPad Pro but none of my

previously purchased music was transferred (100's of tunes); on my new iPad

Pro, the iTunes store tells me I have no purchased music to download. I suspect

it's an authorizations issue but I don't where to find the Apple location where

I can authorize/deauthorize devices. Help!