How do i get my 6 digit code

See -> Automatically fill in SMS passcodes on iPhone

Automatically fill in SMS passcodes on iPhone – Apple Support (UK)

When you sign in to some apps and websites, a one-time SMS passcode is sent to your iPhone. As a security measure, you are required to enter the code into the app or website. iPhone can detect the passcode in Messages and display it above the keyboard.

See also -> Two-factor authentication for Apple ID -> Two-factor authentication for Apple ID - Apple Support