Go to File > Export > Layout As PDF. In the "Export as PDF" dialog box, give a name and choose a location for the PDF file, then press the Options button.
In the new dialog box, for "PDF Style" choose "Press - High Quality. Then go in the left pane to "Color". For "Mode" choose "Separations" and for "Setup" choose "Process and spot". In the list below you can also check/uncheck the wanted/unwanted color plates.
After all settings are made, press OK button, then press Save button.
Another option is to export a composite PDF file, then open it in Acrobat Pro and print the separations in the RIP printer.
Hope this helps.