Removing Mutlisite lines stop DB connection

I’m trying to revert my mutlisite to a single site and following a guide it recommends removing the following

    /*define( 'MULTISITE', true );*/
define( 'MULTISITE', false );
define( 'SUBDOMAIN_INSTALL', false );
$base = '/';
define( 'DOMAIN_CURRENT_SITE', 'www.dreamdoors.co.uk' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

and also to make

define('WP_ALLOW_MULTISITE', true); to false

I’ve commented out the first part and changed the second path but then it says can not find Database connection.