CAD files saved in the Dassault Systems Universal 3D XML format (.3dxml) can be converted to IGES ASCII CAD files (.iges, .igs) using the Export or Save as.. function in CATIA CAD software, or any other dedicated 3D modeling softwafe or converter with the support of .3dxml files.
Considering that 3DXML is a proprietary format, the options for 3dxml to iges conversion will always be somewhat limited.