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Please ensure the system is updated to its latest version. I suggest you follow the troubleshooting steps mentioned below:
1. Restart the system by navigating to Settings->System->Power->System restart
2. Update the system by navigating to Settings->System->System update->Check now
3. Select Settings followed by System
4. Select Zipcode and enter your zip code
5. After you enter your zip code, you need to set up the Live TV input again and let your Roku TV re-scan the "over-the-air" channels.
6. Navigate to Home, and select Live TV. If Live TV is missing, you can add it by going to Settings > TV inputs > Live TV > Set up input
7. Follow the instructions on the TV screen to complete the setup.
For additional information on setting up the Live TV input, please refer to this link: How do I set up the Live TV input on my Roku TV
Hope you'll find this information useful. Let us know in case you've still got any questions.