SolidWorks supports IGES (.igs, .iges) format by default and thus should be capable of exports of 3D parts (.sldprt) to that format. Other programs like Autodesk Inventor can also achieve this and same goes for several other CAD converters. A viable alternative to achieve sldprt to igs conversion would be to use some dedicated 3D model / CAD conversion or translation software or service.
Open SLDPRT file Open IGS fileA CAD viewer program with conversion capabilities
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A dedicated CAD converter