Calendar: Infinite number of repeating events on one day

I’m using the calendar on iPad (2017) and iPhone (15 pro, 2024) and in the standard iCloud calendar (and the calendar on my ipad) there is an all-day event that seems to be repeating an infinite number of times on 20th October. It’s listed as my birthday, but my birthday is not in October. It’s set to repeat yearly, with no end date.

No matter how many times I delete the event, it won’t disappear. If I hide the iCloud calendar I lose all my other events, and it still appears in the iPad calendar. I can’t even book anything else on 20th October so it’s basically wiped out a whole day.

Any ideas on how I can just clear everything from that one day? Instructions for an adult ADHD brain (ie step by step, for dummies) would be ideal, thank you!