specify what your mean when you say "removing terrain".

do you mean digging? do you mean, removing vegetation only?

a mod called, "World Edit Commands" will do both, (as well as lots of other terrain options) but you'll also need a mod called ServerDevCommands for it to function.

https://youtu.be/Bwkb3XadSl0?t=1007

PlanBuild has terrain tools, amongst lots of other things. It'll let you raise, lower, or reset terrain in a fairly large area.

If by "removing terrain" you mean "getting rid of trees, bushes, rocks, and the like," you could just use the "forcedelete" command in console (assuming you are in single player or otherwise have admin access).

Example: would remove all objects in a 50m radius. (It would not alter the terrain itself.)