I found an iphone in a bus

Your uncle shouldn't have given the phone to you to do anything with in the first place. The phone should have been turned into the bus company lost and found, with the hope the rightful owner would have reported the phone as left on the bus.

Apple doesn't get involved in lost devices. And NO, there is no way for you to find the owner.

I do appreciate you wanting to reunite the phone with the owner, but on your own, you can't. At this point, turn it over to the authorities where you live and hope the owner filed a lost or stolen phone report. Chances are if they were tourists, they've given up on the phone and may even no longer be in the country. And if that's the likely scenario, drop the phone off at your closest Apple Store or BestBuy store and they will recycle the phone responsibly.

There is NO WAY for you to bypass an Activation Locked iPhone.

As Bob Timmons suggests, either drop it off at a recycler (Apple recycles phones and so does BestBuy in the US) or drop it off at a police station. It is totally useless to you.

The couple might have called the bus company to ask if someone found the phone and turned it into the main office.

Have you checked to see if there are any messages at the bus company headquarters?

Then, if you have concluded that the owner will never be found, drop the phone off at the recycling center.