This is an iPhone given by my niece unfortunately she forgot the passcode. After restoring the factory settings and setting up my new account it asked again for the old passcode although I chose input passcode later will I be able to reset the passcode even if I forgot the old one?
iPhone X, iOS 16
If you restored it to factory settings it should not need an old passcode. Are you sure it was asking for an old one and not just asking for you to set up a new one? Some features require a passcode be set, so I suspect the default procedure is to set one up immediately. If you do not then you can continue to use the phone but some features requiring security will not be available.
If you are sure it was asking for an old one, what were you doing exactly when it made this request? Apple may ask for other codes in various contexts, such as Two-factor authentication for Apple ID - Apple Support
If you restored it to factory settings it should not need an old passcode. Are you sure it was asking for an old one and not just asking for you to set up a new one? Some features require a passcode be set, so I suspect the default procedure is to set one up immediately. If you do not then you can continue to use the phone but some features requiring security will not be available.
If you are sure it was asking for an old one, what were you doing exactly when it made this request? Apple may ask for other codes in various contexts, such as Two-factor authentication for Apple ID - Apple Support
Resetting passcode even if forgotten old passcode
