How to crop an .fbx mesh

I am attempting to import a photogrammetry-created mesh from Polycam to Unreal Engine. I have an .fbx scene that contains my vegetation asset (a bush), as well as the surrounding area (ground and walls). How would I go about cropping/removing the unwanted pieces to create a static mesh containing only the bush?

Other file formats that the scans can be include .ply or .obj

Any help would be appreciated - thanks!