The following relates to Minimus, Medius, Maximus plans only. For Mega, Giga, Tera, Wordpress plans see here.
Once logged in to cp.blacknight.com
Select the subscription the database is on from the subscription menu on the top of your control panel in http://cp.blacknight.com. Then click on on the 'More services' tab, then click on "Databases" then click on the Database name in question. Here you will see the option to login to phpadmin. If you click the URL beside "Browse database manager". This will open a new window or tab in your browser.
Once logged in you can access the database tables and make your changes.