How to import .ics file to Apple Calendar

On iPhone with ICSKit (recommended)

1. ICSKit adds the event to your default calendar app. So on iOS, make Apple Calendar is set as your default calendar App (Settings → Calendar → Default Calendar).
2. Save the .ics file to the Files app.
3. Open ICSKit.
4. Select the .ics file.
5. Review and tap Add. Events are added to the Apple Calendar App.