Working with terrain from location import

I have imported location terrain and image but am trying to figure out how to work with it:

In the help system it talks about editing the TIN and applying your own image but I can’t see how to do that. Also, the terrain comes up through the middle of the model, how do I exclude one from the other? I want to cut steps into the terrain but can’t see how to do that.

Is there a tutorial for this stuff please?

This might be a good starting point to learn about this functionality, couple links in the article are good to check https://help.sketchup.com/en/sketchup/modeling-terrain-and-other-rounded-shapes