If you’ve ever had a time zone in your Calendar on Mac that you no longer need you probably didn’t see a way to remove it. That’s because Apple does not provide a way in the UI to remove time zones — only the ability to add them. This can be really frustrating, but you’re not without hope. Below are two ways you can do it.
The first way is via the Terminal app. Once you open Terminal just type or copy/paste the below line in to the command prompt and hit Enter.
defaults delete com.apple.iCal ‘RecentlyUsedTimeZones’
This will remove all time zones except your current time zone. Be sure to close Calendar before applying the change. Then open Calendar again and you’ll see just one time zone in the list.
If you have Xcode installed, you can open the Calendar preferences file located in ~/Library/Preferences/com.apple.iCal.plist.
Then search for the “RecentlyUsedTimeZones” key and manually delete the unwanted items within the key by clicking the (-) icon next to the item number. Save and close the file.
I hope this helps solve this problem for you!