Moving my sons account

Hi all.

My son’s device was on the way out, so I got him a new one. I’m trying to move his account onto the new one and seem to just be going around in circles. 

I cant link the account, to anything, so it’s just stuck in limbo. It is going from android to android, both on the play store on the same account. 

Could anyone help me with what I need to do to fix this? 

I have both his ally code and player ID saved, just incase either is needed.

Thanks in advance ☺️