I can get the land editor to appear, it’s the 4th toolbar on the left, counting the grayed out one on the far left, and then the second option down on the creation popup menu.
That produces the following:
From that point on I’m pretty lost. I can get triangles in the ground to appear, and what must be normal lines or elevation controls to appear, but I can’t figure out what to do next to make the land change.
I did manage to make some water appear once, but I can’t duplicate it.