I've figured it out how to add the device manually to mosyle. I found these instructions on Apple's support page.
For Apple TV re-enrolment, after the MDM profile is removed, the device can be manually enrolled in the new MDM solution. To manually re-enrol in tvOS 15 or later, navigate to Settings > General > Privacy, hover over Share Apple TV Analytics, press Play/Pause, then enter the URL of the enrolment profile.