Once this plugin is installed, in the question bank, in the action menu for each question, there is a new option 'Import a new version'. If you choose that, you see a form where you can upload a Moodle XML file containing a single question. If possible (e.g. if the question type matches) then that question is imported as the latest version of this question. (This is different from the standard way of importing questions, which always creates new questions.)