Resetting mailman passwords
If you forget your list password for a mailman list in plesk, you can use the following:
/usr/lib/mailman/bin/change_pw --domain=domain.com --password=password
where domain.com is the domain containing the list and password is your new password.
This will reset the passwords for all lists belonging to a domain.
There is no way to change the password from the Plesk control panel.