I can't remember my old Apple ID

Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID

If you forgot your Apple ID - Apple Support                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

Typically an Apple ID is an email address you have used. If you are currently using a mobile device that is logged into your account, go to Settings and tap your name at the top.

Look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.

This support article describes ways to find your Apple ID --> If you forgot your Apple ID - Apple Support

or go directly to this link --> https://iforgot.apple.com/appleid

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."

Contact Apple for support and service - Apple Support