I have forgot my old apple id how to find it?

Click on this link to read what to do "If you forgot your Apple ID" --> https://support.apple.com/HT201354

Click on this link to read what to do "If you forgot your Apple ID password" --> https://support.apple.com/HT201487

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

Also read about "What to do after [or before] you change your Apple ID email address or password" - https://support.apple.com/HT204071

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."

https://support.apple.com/HT204169

Note an Apple ID is an email address you have used in the past.

See if you can recover the ID/password. Use every email address you can think of.

Apple ID - How to find your Apple    An iCloud e-mail address is an Apple ID.

Apple ID - Find              

If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get an email option if necessary.

Apple ID - Manage            

Apple ID – Forgot Password