iPad keeps requesting to enter my old apple ID

i just bought the new iPad Pro and entered my regular Apple ID to synchronize all the apps. Out of nowhere iPad keeps bringing up my very old Apple ID, that email doesn’t even exist anymore, saying that there are some apps I can download for free. Anyway, I cannot enter the password. I simply don’t remember it. And hat thing pop-up won’t go away. It forces me enter it. It is so annoying and I need help with deleting it