Finally, I found the way to open "Support Generation" window.
I first thought that supports only appears on "preview mode" screen, but it was not.
(I somehow believed that support material only appears in "preview mode".)
When in "edit mode" and not "preview mode", the icon on toolbar launches the "Support Generation" window.
I would suggest developers that it is better to have the lauch icon on toolbar to be disabled when it is not design to work in that mode.