I go to settings, to Live TV & DVR. Get to the page but get no button to set up. Attached image.
Do you have a tuner device either connected to your computer or a network device?
Yeah, HDHomerun Prime. Discovered easily by everything
Please provide a screenshot of the page when you are on your network and you go to my.hdhomerun.com.
Please provide a screenshot of the System Status of the HDHomerun Prime (it shows the firmware version).
Are you logged in with a Plex Pass account?