to scan a hdd in my lan i nedd the syntax to use fsscan.exe
May I know what F-Secure product and version are you using?
If you want to run a manual scan using the command line, please refer this similar KB article which was created for business suite but the example should work for home users.
Scanning a specific directory (downloads directory of the user Foo):
C:\Program Files (x86)\F-Secure\SAFE>fsscan.exe -t C:\Users\Foo\Downloads\