Find the Owner of an iPhone

The only possibility is to tap emergency in lock screen then Medical ID

If there is nothing there then there is absolutely no way to locate the owner or to make the phone usable. You should take it to a the police or an Apple Store. If you are the owner of a cafe or bar or similar then hold on to it in case the owner returns.

If you restored it then you wiped it of any information. If you were able to activate it with a new SIM then it is indeed free of any ownership constraints.

Nobody at Apple or here can help you trace the owner.

You have a choice, hand it in to police who will sell it on, take it to Apple store who will recyle it, or keep it and use it if it is successfully re-activated.

Totally down to your conscience.

You have encountered Activation Lock, which is a theft deterrent service. Only the Apple ID and password that were used to enable Activation Lock can use that phone. Follow the advice already posted.

If you found it on a train, you should have turned it over to the staff on the train.

Turn it over to the police. ASAP. That phone may still be locatable using Find My, even after you attempted to restore it.

If you turn it over voluntarily, you're unlikely to be charged with receiving stolen property. If you don't, and they track it to you, that's a very real possibility.

When a phone is lost the owner can display a message on the screen with contact information. Unfortunately, as you reset it, that, and other options, such as saying “Hey Siri, who owns this phone” and looking at emergency information are no longer available to you. Apple does not get involved in lost/stolen devices, partly because that would be invading the privacy of the owner. And Apple really has no idea who the current owner of an iPhone is.

So you have no options left, other than leave it with the police or the lost and found service for where you found it.