Apple TV Software Update 6.2.1

You should update your Apple TV (any generation) through the on-device update procedure.

Settings﹥General﹥Update Software

If that doesn’t work, then you can restore the device by connecting to a computer for a fresh copy of the system software.

For computers with iTunes, the Restore button option will download the matching software.

For newer Macs without iTunes, the Restore button option will appear when the connected Apple TV is selected in the sidebar of a Finder window.

Restore your Apple TV - Apple Support (2020 version) (doesn’t mention the 2nd generation anymore)

Restore your Apple TV - Apple Support (2015 version of the support document)

This version software is still available on Apple’s servers, so the above should work.