Undo setting a final date (unset)

1. Open the event
2. Click 'Change event picked' (bottom right of the cover picture)
   
3. Deselect the final date(s) by clicking the green 'pin' button (which will turn grey).
4. Click 'Next' and then 'Finalize'.

Since there are no more final dates, the event will be 'open' again. Participants will be automatically notified that the date(s) are no longer final.

Go to 'My events' (account necessary)