I forgot my Apple ID ihow much known its

You are sign in here .  .  .  with your Apple ID & Password.

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

What happens when you use the same Apple ID that you use to sign in here?

See -> If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

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

If you forgot your Apple ID email address or phone number - Apple Support                  

OR see -> Having trouble signing in?

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

See also -> Contact Apple for help with Apple ID account security

Contact Apple for help with Apple ID account security - Apple Support