How do I remove these stuff from terrain?

Make sure you have layering mode off, and then paint the areas you want, with the texture of your choice. In case you’re editing a map with the Scenario editor, of course.

Scenario editor? no… I’m trying to make a terrain mod without these… I don’t know what is this “layering mode” thing and how to turn it off or how to paint areas I want, I’m not a “pro mod creator” I don’t use any external program, I just copy files from other mods and make changes inside of it, but I can’t find a way to exclude these stuff from the terrain (which for me is kinda ugly) and I would like to remove it somehow, how can I do that exactly?

\resources_common\terrain\mask-mod