How do I recover old iPhone password using new iPhone

Are you referring to the passcode to unlock the screen? If so, you cannot recover that passcode. The only thing you can do is wipe the iPhone and the restore your last backup. You cannot recover a passcode on any iPhone. If you are referring to the iCloud password, you can restore that if necessary. See this. If you forgot your Apple ID password - Apple Support

No. The passcode is stored only on the phone itself.