This all assumes the plug connects to your house's wifi, if not let us know how it normally connects
you might be able to find it somewhere in your router's settings
If the plug is already joined to your wifi, then your router will know the MAC address, and you should be able to see it.
look for a page about DHCP, it should show all of the devices on your network, their Mac addresses, and the IP addresses assigned to them. if you're lucky, the plug will be named something you can figure out. If you're less lucky, enough of the others will have names that you can figure out which one it is.