how to repair /smooth a polygonmesh (stl generated from 3D-scan)

Hello Community,
I got a polygonmesh modell. The edges are rough and not clearly defined. My first idea was to use Rhino 5 for repairing the steps manually. But it seems to me it´s a painstaking process (... and by the way, it´s not really intuitiv). I´ve already installed MESHLAB and FREECAD and played a little bit. Depending on insufficent Know-How the results are unsatisfying.

I´m more familiar with nurbs meshes. There is the possibility to blend surfaces in a tangentially or curvature constant way.

The idea for getting nice edges is to cut the polygonmesh with a pipe (along a defined curve) into 2 parts. How to blend the 2 parts ?

Is there a different way for getting a satisfying result?

Thanx a lot for your help
Steff