After creating your event in Boomset go to the "Import a Guest List" tab and select Start Import next to Connect with RegOnline.
As long as you are the main RegOnline account holder and have linked your RegOnline account in your Boomset profile your events should start to populate.
Choose which event you would like to import by selecting Import towards the left of the event name.
Feel free to reach out to us at support@boomset.com in case you have questions or need assistance.