I wouldn’t consider it fixed as it is just simply a bunch of triangulated surfaces due to the STL file format. I recommend obtaining or re-drafting the original CAD file and converting it to IGES/STEP/SolidWorks part file instead. It would be more robust and easier to work it as well.
For this case I imported it into SolidWorks and selected the option that would turn the faces into solid surfaces. Then just simply upload it and you can see what you get. The mesher also tends to not like oversize geometries especially for STL so do take note of that.