You need to …
[spoiler]
1. Get into the bottom floor somehow, e.g. by jumping down the mushrooms on one outside wall of the tower and lockpicking the garden entrance, though there are other ways.
2. Combine a sussur bloom from the garden with the elevator mechanism in that room, then go up a floor to use the lift.
That's just it, I can no longer find the elevator mechanism. It's gone, and just an empty space remains.
