FATAL ERROR , Sommerce Theme [closed]

If you rename the theme folder(via FTP access, or the File Manager on your hosting control panel), that theme will be disabled. That will let you log in as admin, then you can select another theme. That will temporarily make your site look different, but you will be able to recover and select another theme.

As for the cause of the problem, contact the theme developer. Theme (and plugin) support is the responsibility of the theme/plugin developer…and not a question for here.