Install a profile on my Apple TV

Apple TV doesn’t support connecting to networks that require both a username and a password (captive network portal).

• For semi-permanent use (corporate/edu), you can ask the network administrator to install a device profile with these credentials built-in for automatic network sign-on. It will always sign in with these credentials (no user settings), as long as the profile is installed.
• For temporary use (e.g. hotels), you are far better off by using a travel router (non-hotspot) to bridge between the existing network and your personal devices.

Troubleshoot your internet connection. Try rebooting your modem if on wifi

Set up and use multiuser on your Apple TV - Apple Support