org-icalendar-combined-agenda-file

org-icalendar-combined-agenda-file is a variable defined in `ox-icalendar.el'.
Its value is

"~/org.ics"

Documentation:
The file name for the iCalendar file covering all agenda files.
This file is created with the command M-x org-icalendar-combine-agenda-files.
The file name should be absolute. It will be overwritten without warning.

You can customize this variable.