it's usually a bad idea to convert a scanned stl to a body in fusion. there are several workflows you might use, but rarely will direct conversion be the answer. if you post your model, or at least some pics, we can give you some ideas on a direction.
@Monodon wrote:
...I need to make a body from it to perform substract etc operations.
not necessarily. instead you can convert bodies made in fusion to meshes and do the subtractions in the mesh environment.
