If the account is set up with secondary authentication in which three answers for respective questions , date of birth , rescue mail address and its password is added .
In case if you are having incorrect credentials .
And Apple ID is signed in iPhone convert the account in 2FA Two-factor authentication for Apple ID - Apple Support
Get a verification code and sign in with two-factor authentication - Apple Support
If the Apple ID is not signed in iPhone contact apple support Contact Apple for support and service - Apple Support
( a ) if you have lost Apple ID password provide invoice copy of Mac to apple support advisors .
( b ) Contact apple support , they will send a link on mail account , click on link after 24 hours to reset apple id password , however the link is valid for additional 3 hours .