Change phone number

See If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled  https://support.apple.com/en-us/HT204306, especially the section entitled Remove your passcode. 

Remove your passcode says if you don't have a computer to use, then "borrow one from a friend, or go to an Apple Retail Store or Apple Authorized Service Provider." Of course the last option usually is not available now.

Later the document says: "If you can't update or restore your device using recovery mode, or you can't use recovery mode because of broken or stuck buttons, contact Apple Support. Then follow the steps to set up service for your iPhone, iPad, or iPod touch." 

_________

But you mention password. So,

See If you forgot your Apple ID password https://support.apple.com/en-us/HT201487

You also can use Having trouble signing in/iForgot https://iforgot.apple.com/password/verify/appleid to try to recover your password.

And you undoubtedly will need to see If you forgot the answers to your Apple ID security questions https://support.apple.com/en-us/HT201485