Lost access to my account - Can’t login

After having changed to a new iPhone (iP 16) I wanted to used the IMDB app on that. I’ve used the alternative “log in with Apple” but that didn’t work. I was all the time prompted to “Register an account”. Okay, thought I needed to logout from the app on my old iPhone (iP 8). Did that but same symptoms: Couldn’t log im with Apple, pasting the Apple-created email address didn’t work either. So now I couldn’t login on either my iP 8 or my new iP 16. With the hope that it’s only I corrected promted I proceeded with login and create an account and sure, that worked but it’ a new blank account. How can I get my old account back, with all my ratings etc.?