Here are 2 good tutorial on dealing with 3d scan.
I have been trying to figure out a good workflow for 3d scans, still working on that.
First thing is you want to make sure your model is solid, Shapr as far as I know can’t do that. You need external software like Blender, I been searching through this forum on 3d scans to see how I can add Shapr into the workflow but not much out there other than using 3d Scan STL as reference model to rebuild.
Since you just needed a negative/mold working with mesh tool, like ones mentioned will help you.