I happen to have that tgd as well, so took a look. It's indeed a cloud layer that makes the ring: Cloud layer v2 01_1. If you disable that, it'll be gone.
And with the canyon; the Constant scalar 01 is the size of the voronoi (flat) mountains, so increase that and the whole patches of hills get larger, and so are the gaps/valleys. The Distance between canyon walls really doesn't have much effect, it's just a small adjustment to the curve.
For height you have to check the settings of the Tile Profile, which has a displacement multiplier (at 4000). Increase that and hills are higher.
If you really need to change the gaps, but not the size as such, I'd advise adding a color adjust shader as shown. With the black and white values you can change the appearance of the mesas much better. From -0.5 for black and 0.5 for white for small gaps, values 1 and 2 for really wide canyons. Play with those values. A Blue node called smooth step would even be better, with two constant colors attached, as that gives the edges a slightly rounded effect, while the color adjust gives a hard edge.
It's good practise when studying a file like this to disable one node at the time and see what happens. See what settings are there, try changing one of the settings at the time bigtime, and see what happens. Then you get to understand the line of nodes, and each setting.
Good luck, and do post results of your endeavours. All begin is hard, especially in TG.
