iPhone 6S Plus

I bought a second hand iPhone 6S Plus the other day, it looked to be ready for me to set up the iPhone, but when I got home to try it, there was a screen saying, "This iPhone is currently linked to an Apple ID (S*****@hotmail.com). Sign in with the Apple ID that was used to set up this iPhone." So my question is, how can I get by this? I don't have the sellers information, so I can't contact him. Please help me sort out this problem.

Thank you.