The Error Establishing Database Connection error means that your wp-config.php file doesn’t contain valid database credentials.
Edit your wp-config.php file and you'll see the database settings section:
// ** MySQL settings - You can get this info from your web host ** //
/** The name of the database for WordPress */
define('DB_NAME', 'SCWORDPRESS-33426930ea');
/** MySQL database username */
define('DB_USER', 'SCWORDPRESS-33426930ea');
/** MySQL database password */
define('DB_PASSWORD', 'eb07bfe05d3240-example');
/** MySQL hostname */
define('DB_HOST', 'wordpressdb-i.hosting.stackcp.net');
Ensure all four sections correspond to the database details on the Black Owl hosting package via the MySQL Databases page: Manage Hosting > Choose Package > MySQL Databases.
You may wish to take the password in the wp-config.php file and set the database password to the same one to ensure it matches.
After saving the wp-config.php file, refresh the site and the site should connect to the database successfully.
If you're still having connection problems, please raise a ticket with our support desk by emailing support@blackowl.co.uk.