I've linked more than one Nintendo Switch console to my account on the Nintendo Switch Parental Controls app, but I'm not sure which is which.
You can change between the consoles that have been registered to your account on the Nintendo Switch Parental Controls app by touching the icon with a plus symbol in the app.
Touch the "i" (information) icon to check the serial number for each linked console.
On the console, you can check the serial number by opening System Settings on the HOME Menu and selecting System ⇒ Serial Numbers.