The file should be found at <projectdir>/data.csv.
I am sure you would find it by Windows Explorer, or Mac Finder.
Do you want to see it in Katalon Studio?
While KS GUI opened, try F5 (Refresh). But, I know quite often the “Refresh” operation does not work in Katalon Studio GUI. See another post
In that case, you should close the project once, and reopen the project.