Thanks for posting here in the Google Nest Community and sorry for the delay.
I know how it feels when something isn’t working as it should, so let’s get this resolved. What message are you getting every time you try to link the Nest app to your TV? Does your TV have Built-in Chromecast or Chromecast device plugged into it? You can try to reboot your TV to refresh it then try it once more.
Check this helpful link for more information.
Let me know how it goes.