How to resume the phone with another account?
Bought iPhone 5s with the hands, the former owner does not remember the password from the App Store without it I can not use the phone. How to resume the phone with another account?
iPhone 5s, iOS 9.2
Following are instructions on what to do before selling an iPhone: What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support
The bottom part has a section on what the previous owner can do when he no longer has the device. If he doesn't remember the password for the Apple ID, he can get help from Apple for that: If you forgot your Apple ID password - Apple Support