How do retrieve my forgotten Apple ID? – Apple Community

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 …

https://discussions.apple.com/thread/255914210