Hello I forgot my Apple ID date of birth, please help me

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

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

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

If you forgot your Apple ID - Apple Support                  

OR see -> Having trouble signing in?

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

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See this Apple article: If you forgot your Apple ID password

If you forgot your Apple ID password - Apple Support

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

B T W:

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 & Password that you use to sign in here?

See the following Apple articles

Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

Read this support article about how to update the birth date associated with an Apple ID: Update the birth date associated with your Apple ID - Apple Support