If you can’t change a calendar or event on Mac
If you can’t change an event you created, or you can’t change your status for an event you were invited to, it might be because you’re using an email address in Calendar that isn’t on your card in Contacts. Make sure all your email addresses are listed on your Contacts card. See Edit contacts.
You can’t change events for calendars you subscribe to, although you can change the calendar name, colour, location, and whether alerts or attachments are removed.
You can’t edit a calendar for which you have view-only privileges. To check your access privileges, place the pointer over the calendar’s name in the calendar list, then click the Share Calendar button . If you see View Only next to your name, you have view-only privileges. (If you don’t see the calendar list on the left, choose View > Show Calendar List.) See Ways to share calendars.
If you were invited to an event, you can change only some settings: your status, the calendar where the event appears, the alerts and your availability.
You can’t change birthdays in the Birthdays calendar in Calendar; change birthdays in Contacts.
If you can’t change the time zone for events, time zone support might be turned off. In the Calendar app on your Mac, choose Calendar > Preferences, click Advanced, then select “Turn on time zone support”. See Use different time zones.
If you want to change events on a published calendar, but you deleted the calendar, re-create the calendar with all of its events, give it the same name, then publish it. The new calendar replaces the previously published one.