How to reset "JFBCLike module" 's counter?

Luca,
There's no way to change the count of the Like buttons. Those button stats are all stored on Facebook's servers, not your own. The only way that you can 'reset' the count is simply by changing the URL of the page, which is what Facebook associates the Like count with. So, if you tested your site on a different server and move it 'live', that will effectively reset your count. Once it's online though, there's no easy way to do it unless you want to use the {JFBCLike href=xxx} tag and simply specify a different URL (or add a new query string parameter, etc) to make Facebook think that the Like is for a different page.

Hope that helps explain, but if you need anything else, just let us know!
Alex