The easiest way to delete a recurring event is by deleting the first occurrence.
Since the first occurrence can be pretty far in the past adding a button to the Tools menu first might be convenient.
This is a one time job only.
Add Action Menu Button
- Go to Settings (tap gear button)
- Select Tools
- Select Add Menu Item
- Add Go to 1st Occurrence (scroll down to bottom)
Delete Recurring Event
- Select a random current event of the sequence to delete
- Press the Tools button at the bottom
- Tap Go to 1st Occurrence
- Pres Delete button and select Delete All Future Events.