To login to the control panel, please use the “Control Panel” button in the client area.
Most likely you messed it up, so click the edit settings button on the account viewer in the client area and change the account password. Wait 5 minutes, then click the “Control Panel” button again.
If you install SMF (or any other software) through Softaculous, then you may find the admin credentials of your site in the Installation Details page in Softaculous
If you installed the site by hand, then we don’t have credentials for your site at all. Some sites use some sort of default password, but most ask you for admin credentials during installation.