how can I update my apple TV with computer. Cannot start apple TV

Do you have an Apple TV box? If so, which model? Identify your Apple TV model - Apple Support

When connected to power, does the status light glow continuously (after ~15 seconds)?

If your Apple TV doesn't turn on - Apple Support

Hello mishra241, Apple TV does not connect to a computer or Apple iMAC computer. See this Support page for Setup.

Set up Apple TV - Apple Support