tvOS 13.3.1, which is a free update, can be downloaded over the air through the Settings app on the Apple TV by going to System --> Software Update. Apple TV owners who have automatic software updates turned on will be upgraded to tvOS 13.3.1 automatically.
tvOS updates are usually minor, focusing on under-the-hood bug fixes and improvements rather than significant outward-facing changes. Apple provides limited information on what's new in tvOS updates, and we didn't find new features during the tvOS 13.3.1 beta testing period.
Details on the update will be provided through Apple's tvOS support document.