Hello Sky_hie,
there are many options to realize this:
1. Select unwanted object in the model and delete the surfaces. Then: Tools -> Mesh -> Close holes
the better one:
2. Once the dense point cloud exists, you can mark the points (Free from selection tool) of the object and delete them. Mesh generation you run in height field mode and interpolation enabled. The hole will be closed with an interpolated surface from the borders.
3. You can mask the object in photos, then Tools -> Dense cloud -> select masked points. Further like in point 2.
4. You also can classify ground points (Tools -> dense cloud -> classify ground points). In mesh generation you have to use only the ground points in class selection, so only the ground points will be triangulated.
best regards
Paul