HOW TO CHANGE APPLE ID WITHOUT OLD ID

Your Apple ID is generally an email address (in a very few countries it may be a phone number)

You may have used your old Apple ID and password to log-in here to the community.

Check if you are using your old Apple ID for Messages or FaceTime or iCloud etc.

Also: check if you are already logged in (to your iPad) with your old Apple ID:

Sign in with your Apple ID - Apple Support

Else: See if you can recover your old Apple ID and password:

What to do: If you forgot your Apple ID - Apple Support

and

If you forgot your Apple ID password - Apple Support

Then:

How to change your Apple ID to a different email address:

Change your Apple ID - Apple Support

and

Change your Apple ID password - Apple Support

If needed:

Apple ID support website: (info. / support / contact options etc.)

Apple ID - Official Apple Support