Again... irrelevant. There is nothing wrong with his phone. It's an Apple account issue.
The phone is activation locked with the Apple ID and password he can't remember right? Does the phone look something like this...
Or is it his passcode that has the phone locked?
For activation lock, if he has forgotten both, he will have to make a new one, and the data on that phone is lost to him. To unlock that phone, he will have to provide the proof of purchase to Apple by phone (and then email) and they will determine if they can unlock it.
There is no physical repair required for what you are describing to us. Warranty is irrelevant. That you're in China is irrelevant. This can be done by phone.
If it is his passcode, that can be reset using these directions, but you may still run in to the activation lock after removing the passcode.
If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support