How to factory reset a locked iphone 6?

So I bought an iphone from a seller on eBay. It's in great condition. However, they didn't factory reset it before sending it to me so I need their pass code to unlock and use it. I've messaged the seller, no response. Searched the name on the return address and judging by pictures on Facebook and the background photo on the phone, I highly doubt it's stolen or anything like that. I think it's just they honestly forget to reset it and don't check their eBay messages very often.
so my question is, is there a way I can reset the phone WITHOUT the pass code? I've tried restoring it on iTunes but it says it can't connect because it needs the pass code.
I could message the person on Facebook, but I don't want to come off as creepy and invasive

You can't do anything without the passcode, not even Apple can. When you upgrade to a new phone they make you factory reset it for this reason.

A couple of years back the FBI was trying to crack an IPhone passcode and they couldn't do it either.

Unless you get the passcode you bought some useless hardware sorry. Trying to guess the passcode will end up locking the phone completely, which is why the FBI couldn't crack the phones passcode.

Sure you did. You found it and now you want someone to teach you how to steal it.

Well there's no way to unlock it since the pulse nightclub shooting. Imagine how embarrass apple must be when someone was able to crack it. So apple made it even harder to crack.

You need the passcode, PERIOD. There's no way around it, which is what Apple wanted. NOW all those lost and stolen iPhones with passwords are pretty much useless to the finders, so they sell them (stolen ones), which is why they tend to sell them as fast as they can.

So contact them by their Facebook info if that is all that you have, as far as contact information, and let them think what they want, you can't use the phone, they sold you and if you wanted your money back, how would you contact them, had they sent you a shoe, instead of a phone?

Can't.

Even if you got around that somehow you'd run into iCloud Activation Lock which would require the Apple ID's password.

If you can't contact them & I'd contact eBay on either contacting them or looking to get a refund.

You have been scammed.