In your fonline folder, there will be paths for your critter/master dat's.
Make sure your data browser can see extensions, like .txt .cgf, so you can change it, or else you'll just make it's name ".cfg" in the end.
Edit:
Write path there manually, for example:
X:\FOnline\MASTER.DAT
X:\FOnline\CRITTER.DAT
Or run 2238 config and put it there.