If you forgot your password, provide your email address and click on Spediscimi via email i miei dati. The button is only available if the wiki has been configured to support email.
The email you get contains the encrypted password (so even if someone intercepts the mail, he won't know your REAL password). Just copy and paste it into the login mask into the password field and log in.
Then change your password to a known value and save your settings.