Hi Daniel,
I don't know if this is the easiest way to do this, but i usually do the following for this issue.
1. you need someone that is in the reoccurring event.
2.1 or add the calendar from someone that is in the event as an admin then open de debug link.
3. click on the event and then the 3 dots next to the bin icon, scroll down in the menu to the troubleshooting info and open this.
4. you'll see the event ID behind the eid= in this window. you only need the ID between = and _ (show in bold by the xxxxxxx eid=XXXXXXXXXXXXXXXXXX_20231003T073000Z )
5. use gam to delete the event ID for the users gam user <USER MAIL ADDRESS> delete event id <EVENT ID> doit
if you dont want to do it by hand for each user, use gam all users delete event id <EVENT ID> doit