I need to reset my password and username

In your phone open Settings app

At the top if the page is your name. Tap on it for your apple ID.

(Or refer to the article at the top of this thread.)

then

if you forgot your Apple ID password

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

Forgot ID password: https://support.apple.com/en-us/HT201487

Forgot Apple ID: https://iforgot.apple.com/password/verify/appleid

Do you mean you bought a phone that is locked to another Apple ID?