I only use a single profile, so what I am going to say may not work in a multi-profile situation. The most complete way to set KM back to the defaults is to exit KM and rename the folder 'Profiles' in KM's root directory to 'Old_Profiles'. When you start KM again everything will be created new. Also you have a way to return to the old profile by just deleting the 'Profiles' folder and renaming 'Old_Profiles' to 'Profiles'.
Exactly how I do it. Saves a lot of headache (but I also zip up the entire browser folder(s) as a secure backup.