I am not sure what you are wanting to do?
Do you want to disable your Wifi?
If that is what you are wanting to do you, You simply untick the "Enable Wireless Radio" for both the 2.4Ghz band and the 5Ghz Wifi band.
Are you getting any error?
If your smart TV has a built-in ChromeCast, then it should just automatically detect your home Wi-Fi.
I would recommend to check the TV's Manual on how to connect or set up the connection for your TV.
You won't need to disable any setting or feature on the modem.