How to convert igs file into 3ds file ?

I can convert an igs to an OBJ. If that is helpful, let me know.
3DS files I am not familiar with. Are those 3d studio max?

Use any CAD program like FreeCAD, SolidWorks which supports *.igs and *3ds. Import *igs into that and then export in *3ds. I Think it should work though I haven't tested it.

There are many Online convertor which convert CAD file format from one to other. or you can change through CAD Software offline

Freecad can do it. It opens IGES and exports as STL or OBJ.