You have indeed multiple options in the appstore. This one has been a steady one: https://appstore.home.mendix.com/link/app/429/Erwin-'t-Hoen/Flat-&-delimited-file-import
The maker is here often in the forum so if you run into something you probably get an answer soon.
Other one to look for is this one: https://appstore.home.mendix.com/link/app/108605/Mendix/CSV
May be not in your case since the amount is limited that you need to import.
And have you thought about how you retrieve the files? Do users upload those or do you need a way to transport the files?
SFTP is always a good option. There are a couple of sollutions for that in the appstore. Or create a web or REST service for it to proces the files.
Good luck and regards,
Ronald