You can remove an entire event but you are unable to edit an event once it has been created (i.e. end it earlier or make changes to the times). You can remove a recurring calendar event by tapping on any date of the event:
If this is not working, please check to ensure you are using the most up to date version of the app. If this doesn't work for you, we are also happy to help you with this task. Please send an email to firstname.lastname@example.org with the name and dates of the event and a member of our support team will remove this event from your calendar.