Pretty good non-verbal video that shows you everything. They are adjusting by the yellow marks at the bottom of the cassete joint, there should also be a pair at the top with one behind a clear plastic window that would be more easily seen (though maybe harder to get on video) once the wheel was in the bike.
https://www.youtube.com/watch?v=qpHQdSvLQj8
Pretty good non-verbal video that shows you everything. They are adjusting by the yellow marks at the bottom of the cassete joint, there should also be a pair at the top with one behind a clear plastic window that would be more easily seen (though maybe harder to get on video) once the wheel was in the bike.