Factory reset Samsung Galaxy J3 (2017) without power button or pin

I bought a second-hand Samsung Galaxy J3 (J330FN) last week. It arrived today, missing a power button (which I was not informed of beforehand) and not factory reset. The seller is trying to be helpful but has forgotten the PIN... naturally. The phone does not offer power options from the notification shade, so I seem to have literally no way to power it off, or better still get it into fastboot mode in order to initiate a factory reset. I have tried connecting it to my PC with the Samsung USB drivers installed but ADB cannot see the device in order to send commands to it, understandably since I cannot unlock it to enable developer options and USB debugging! Catch 22. Anybody have a lifeline here (short of me asking for a refund)?