So this mesh is open and not aligned. If I needed to work with this mesh, I would align the mesh on the XY plane in the scanner postprocessing software.
To define a CPlane on your mesh, I duplicated the naked edge points and fit a plane through the points.
I selected the naled edge by holding ctrl+shift and double clicked on one edge segment. This selects the entire loop. I extruded the naked edge downwards beyond the local CPlane.
Then split the mesh with the plane surface, deleted whatever is below the plane and ran _FillMeshHoles.
The result is closed.
