My old apple id and my ipad

My ipad and icloud are connected using an old apple id.

Unfortunately, that old one is no longer valid.

So I can't sign out of icloud on the ipad, and I can't delete the account either, because doing either requires a valid apple id and password.

Any ideas how I can break this connection so that I can set up again with my valid apple id?

Thanks for any help!

ipad

version 9.3.5

60GB capacity