Programs enabling conversion of the file:
If your objective is to convert the file from ICON to the file ICNS, you can use any of the applications listed. ICON to ICNS conversion process in every program intended for this purpose (so-called converters) is very intuitive and everyone is able to manage converting a file.
However, bear in mind that the list may also include programs to support and work with the indicated extensions ICON and ICNS - and not only converters. In such a case, you need to open the source file ICON and from the options available in the program, choose ”Save as... ICNS" or "Export to ICNS".