In the mobile app's devices you see a list of devices that are connected to your network. Many will have a name that is specific to the device but those that the system is not able to identify are listed as "Unknown_" + the devices MAC address (media access control address). A MAC address is a unique hardware identifier that consists of a 12 characters that is generally displayed with a color or hyphen serpsrating every 2 characters. The MAC address is often printed on the label of the device.
You can give your device a different name in the app by tapping on it and editing the name on the device details screen (available with some configurations).
How to Find MAC Address on Windows, Mac, iOS, Android, Linux: