On your iPhone: open Calendar › Calendars › tap ⓘ next to a calendar › turn on Public Calendar › Share Link › Copy Link, then paste it here. The Daybook checks it every few minutes. Anyone with that link can see the calendar.
To get a file from Apple Calendar on a Mac: File › Export › Export…
Calendar files can't be saved from inside Claude. Open The Daybook from its own web address and this button sends events straight to Apple Calendar. For now you can copy the calendar data.