Hi there,
You will need an external Alexa device connected to your U7900 TV to utilize a voice assistant.
To access local channels, run Auto Program to scan for available channels: Settings > All Settings > Broadcasting > Auto Program.
Should you need more help, we're here for you. You can reach us at 1-800-SAMSUNG (8AM – 12AM EST, 7 days a week), or connect with a LiveChat agent by selecting ‘Support’ on our website.
~ Samsung Advisor