From IDF support:
The file you need to delete is "identityinfo.dat" and is located here:
Vista/2008/7 -> C:\Users[USERNAME]\AppData\Local\Identity Finder\identityinfo.dat
2000/XP/2003 -> C:\Documents and Settings[USERNAME]\Local Settings\Application Data\Identity Finder\identityinfo.dat
Where USERNAME is the name of the user account that needs a password reset.