How to edit or delete Yahrzeit date imported into Google Calendar

After importing a yahrzeit calendar into Google Calendar (by downloading an ics file and importing it into Google Calendar), I realized I had entered one of the yahrzeit dates incorrectly when creating the calendar in HebCal. I corrected the mistake but couldn't import the corrected yahrzeit calendar into Google Calendar without first unsubscribing from the first yahrzeit calendar. Importing the corrected yahrzeit calendar worked, except that I now have two dates for the affected yahrzeit: the original, mistaken date and the corrected date.

How can I delete (every occurrence of) the mistaken yahrzeit date from Google Calendar? When I click on the entry in Google Calendar, editing and deleting are not options.

Thank you in advance for your help.