How can I remove the lock of a given iphone

I have a friend who gave me an iPhone. Supposedly he upgraded to a newer version so this one he gave its his old.

However, he didn't give me the password to unlock it and I've been trying to contact him but he's not responding. That makes me feel suspicious of the iPhone even though I never knew him to do sketchy business. I connected it to the wifi but nothing has popped out of screen like lost mode or whatever. What should I do?