Having problems with changing my Apple ID on my ipad

I keep trying to sign in to my Apple ID on my iPad that I won at work last year. It was set up under my old work Email that I no longer have access to. When I put in the new ID from my new phone it says “this email is already in use”, and let’s me go no further. I don’t know much about apple products but I have had issues with both my phone and iPad signing in to something as simple as downloading apps