Things to prepare:
USB Type-C to RJ45 Adapter,
RJ45 Cable/internet cable
Router (with Internet)
1. Plug the Rj45 cable to the router.
2. Connect the Rj45 cable to the adapter.
3. Connect the adapter to your phone (with USB C Port that supply OTG).
4. Now check the notification and if you see the "Ethernet cable connected" on your phone, then set up the configuration.
4.1.If not, you have to go to Setting -> Connections -> More connections settings -> Ethernet -> Configure Ethernet device. Before connecting the device, you have to configure, otherwise, you can not figure the device's IP address. Recommend choosing the DHCP, with auto-config -> None.
5.Then enable the Ethernet. (Don't forget to turn off your mobile data.)
6.Next, check the indicators on the adapter if it is blinking.
Finally, you are good to go.