This happens when you upload fresh cms_config.php, and by instructions you should edit file on server not upload fresh/new one from not installed script.
Looks like you overwritten your application\config\cms_config.php with new file.
If you have old, then restore and upload old.
If not then you can open it and change:
$config['installed'] = false;
$config['installed'] = true;
If you also overwritten database configuration, then populate it again in application\config\production\database.php