I wonder if I'm missing it somewhere but can you customize the columns in backend view? Here for example administrator/index.php?option=com_eventbooking&view=registrants
You can add the custom fields but can you change the order of the columns? Or hide some columns? Or would it need an override of a specific file somewhere?
It's not configurable. So you will have to customize code in the file administrator/components/com_eventbooking/view/registrants/tmpl/default.php
Once the change is done, you should move the modified file to administrator/templates/isis/html/com_eventbooking/registrants folder so that the change won't be lost when you update to future releases of the extension