How can I delete duplicate Calendar events on my new iPhone?

I recently got a new iPhone and when I transferred all my calendar events, it’s now showing a bunch of duplicates of the same event. And having to individually delete each event is driving my ocd up the wall. Is there a different way I can delete all these multiple events? I tried the “delete all future events” option but it doesn’t seem to be working.

[Re-Titled by Moderator]

Original Title: new phone with multiple duplicate events help please