In the latest update to our various apps (available in the next few days) a filter has been added to the “iOS Calendar Events” view accessible from the “Events + Appointments” topic view.  Tapping on  the filter icon will present you with a list of filter options including “Left Over Items” and “All App Items”.  If you choose either of these a delete button will be present in the view.  The delete button provides a means for deleting iOS calendar events that were created by our app.  A popup listing all the iOS events will be presented and all the items will be checked off  but you can unchecked the items you do not want included in the bulk delete of these items.

Until our updated apps become available here are instructions to easily delete the Calendar items in the mean time:

If you have access to a Mac, in the Calendar app on the Mac, there is a search field towards the top right. If you type in our app’s name (such as My.Agenda for example), then all the calendar items created by My.Agenda will show up (since they all have the term [My.Agenda] in their title). You can then click on the top one, then shift-click on the last one (in the search results window) to select them all, then either right-click to delete, or press the delete key on the keyboard.

In some cases the user may have deleted an item in our app but the corresponding linked iOS calendar event still remains.  This may result in the user being constantly reminded to complete these tasks/appointments.  The reason for this may be because when you have our app’s  sync enabled, and when you delete the item in our app from the 2nd device and if the iOS Calendar items are not yet sync’ed (via iCloud) to the 2nd device, then our app on your 2nd device does not get a chance to delete those iOS Calendar items.

Note that when you delete the items in our app, the corresponding iOS Calendar items should be deleted as well. If you delete the app itself, it never gets a chance to delete those entries in the calendar app.
You could also disable the creation of iOS Calendar counterparts for tasks/appointments, etc. from our app > Settings > My Settings > (scroll to the bottom) iOS Calendar Reminders.