ICLOUD DOWNGRADE

Do you mean you created a completely new APple ID and signed in with that? In that case you won't have access to your iCloud account for obvious reasons: you will need to sign out and sign back in with the new ID in order to access your iCloud settings and downgrade it.

Or doe you mean that you kept the ID but changed the email address which constitutes its login? In that case the ID is still the same, but iCloud may be expecting the old login. Try using it to log out, then log in eith the new ID and preceed from there.

You will need to contact Support: they will need to confirm that you are actually the owner of the Apple ID linked to the iCloud account, for obvious reasons. Apple Support

Do what I suggested in my first paragraph above.