Apple ID
The account you use to access Apple services such as the App Store and iCloud. It includes the email address and password you use to sign in as well as all the contact, payment, and security details you use across Apple services.
If you forget which Apple ID you use with iCloud, do any of the following:
On a Mac: With macOS Catalina 10.15 or later, choose Apple menu > System Preferences, then click Apple ID (to the right of your name). With macOS Mojave 10.14 or earlier, choose Apple menu > System Preferences, then click iCloud . Your Apple ID appears below your name.
On an iPhone or iPad: Tap Settings > [your name]. Your Apple ID appears below your name.
On a Windows computer: In Windows 7 or later, click the iCloud app or tile on the Start screen, or choose iCloud from the Start menu. Your Apple ID appears below your name.
For more information, visit the Apple Support site.