How to import STL into Lumion?

I have a file in .stl format and I'm trying to find a way to convert it into a file readable by Lumion, but I'm not progressing much. I tried applying the stl4su.rb plugin into Sketchup so I could import .stl files and export it into .skp to make it Lumion-compatible, but it didn't function either. Does anyone here know a way to convert .stl?

I'm a highschool student experimenting with stuff here, still very new to the CAD business.