Along with iOS 11.2.1, Apple released tvOS 11.2.1 on Wednesday. The update is the second half of Apple’s strategy for patching a security flaw that could let hackers slip through HomeKit’s security measures.
Apple patched the flaw on its servers last week, but had to disable remote access for shared users. Today’s updates restore full functionality for shared users.
To install the tvOS update go to the Settings app on your Apple TV and go to System > Software Updates.