Public Calendars can be managed by multiple admins. You can invite people to become admins via invitation URL links.
- Tap the three horizontal lines in the top left hand corner of the screen
- Swipe this menu to the left once to find your public calendars
- Open your public calendar
- Select "Options" by tapping on the three dots in the top right hand corner
- Select "Calendar & Member Setting"
- Select Member
- Select "Invite" and share the URL via LINE, Facebook Messenger, Email, Twitter.