When I was editing the double basement, I used CFE cheat code. In the end when I finished using the Level Terrain tool, it turns out to be like this

THE ONE I DON'T WANT IS THE LITTLE TRIANGLE IF U SEE CLEARLY
So anyone please tell me how to do that?

Try saving, exiting and then reentering the lot.

Mootilda, U R GREAT!!!THANX!!!

First try to switch to your desktop (if in full screen mode) or minimize the window then run an other window (explorer for example) sometimes it works ant it is faster than save-quit and re-run

If they are what I think they are.. the little triangles are part of the wall, usually it's where walls join at different angles or you have corners and such. I've noticed it mostly occurs for me whenever I'm using the CFE cheat to adjust the height of walls.

You can usually fix it by temporarily deleting the walls under where the triangles are then undoing the delete, or you can use the wall tall and hold down CTRL to drag and remove a line of wall but you don't actually have to remove it.. just run the tool down the affected area so the wall shows it will be deleted then press escape to cancel the delete (or drag back to the starting point) and it should get rid of them