Hello Damigora and welcome to Apple Support Communities.
I see you're trying to change the default app for .ics files back to the Calendar app on a Mac after having changed it to Outlook.
1) Select (don't open) a .ics file in the Finder.
2) Hit Command + I on the keyboard or select Get Info from the File menu.
3) You'll see an Info window for that file. About half-way down, there is a section called "Open with." If it is collapsed, click the triangle next to it to expand the section.
4) You'll see a clickable drop-down menu listing the current default app for the file as well as other options. Change that to Calendar.
5) Click the button called Change All... This will set Calendar as the default app for all .ics files.
Cheers.