tvOS betas are more difficult to install than beta updates for iOS and OS X. Installing the tvOS beta requires the Apple TV to be connected to a computer with a USB-C to USB-A cable, with the software downloaded and installed via iTunes or Apple Configurator. Those who have already installed the first tvOS 9.2.1 beta will be able to update to the second beta over the air.
As a minor 9.x.x update, tvOS 9.2.1 likely focuses on bug fixes and performance updates to address issues discovered since the release of tvOS 9.2. No new outward-facing changes were found in the first tvOS 9.2.1 beta, but should any new features pop up in beta 2, we will list them below.