Alas, we have not found any specific information about kml to igs conversion, beyond the fact this might a 3D model export, typically of terrain or topography maps. Many 3D modeling tools or even CAD software supports Google Earth's KML/KMZ files nowadays, so it should be hard to find a tool that can read the data, but export to IGES format is probably done for specific purpose.
Updated: September 25, 2023