Go to Events Booking -> Configuration, there is a config option called Generate ICS file? Set it to Yes and when someone registers for the event, an ICS file will be generated and send to them so that they can add event to outlook. Will that work?
Another option is going to Events Booking -> Configuration, look at Themes tab, set Allow Save Event To Personal Calendar config option to Yes. Then for each event, there is a Save To button which allow saving event to Google Calendar, Yahoo Calendar and ICS file (like on our demo site joomdonationdemo.com/eventbooking/ ) That should work, too