How to clean up messy geometry from a file?

 From:  Frenchy Pilou (PILOU)
9208.2 
Just add 4 cylinders to the moi3D form yet a "solid" : Boolean Union, resize as you want, export as stl or OBJ ?
but maybe i don't understand the question! :)

EDITED: 11 Jan 2019 by PILOU