How do I access my forgotten Apple ID?

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

If you are logging into Apple Communities then you can use that ID. If you are using another ID as you state "forgotten" then getting it back solely your responsibility.