@DevilinPixy has a rather thorough write up on it from last year and it’s still pertinent .
ihleslie on Steam (@ianh here) has continued work on his program to remove terrain edits. The process is planet wide in its effects. Requires use of the No Man’s Sky Save Editor and his program.
Poofer on Steam has a guide which just utilizes the No Man’s Sky Save Editor but is a bit more complex.
I’m terrible with the use of the Terrain Manipulator. I used @ianh 's method to clean up all of my old terrain edits with the exception of my old bases. When I recently moved (copy/delete) my current base it left a large footprint in the old site and this fixed it.