How to Install a LAN Adapter to Nintendo Switch
Important
Nintendo Switch systems support the Wii LAN Adapter (Model RVL 015) and officially licensed LAN adapters.
Note: If using a Nintendo Switch dock with a built-in LAN port, a USB LAN adapter is not required to establish a wired internet connection.
Complete these steps
Insert the LAN adapter into the USB port on the Nintendo Switch dock.
Connect one end of an Ethernet cable to the LAN adapter, and connect the other end to a network port on your modem or wired router.
Important: Ensure that you have connected the LAN adapter into a LAN port, and not the Internet/WAN port. In most situations, routers will have multiple LAN ports which may be numbered (e.g. four ports labelled 1 through 4).
A LAN Adapter plugged into the USB port on the Nintendo Switch dock by an Ethernet cable from the modem or router
When connecting directly to a modem
Remove any other devices that are currently connected to your modem, including any devices connected with a USB cable.
Power cycle your modem by unplugging the power from your modem for 30 seconds, and then plugging the power back in.