In the Calendar app at the top of the screen.
Add the event details (title, location, travel time, attachments, and so on).
Enter the start and end times for the event, then tap Time Zone.
Search for a location, tap it, then tap Add.
Note: You can edit the time zone of the event later if you need to.
You can override the default time zone setting so you can display Calendar in the time zone of your choice. This can be helpful if you’re working remotely and need to keep track of the time when scheduling meetings with your colleagues in a different time zone. For example, if you live in San Francisco, but your job is based out of Boston, you can override the time zone of your current location and view your calendar events according to the time zone in Boston.
Go to Settings Set up multiple calendars on iPhone