The phpMyAdmin tool available in cPanel is bundled with it and can be used only if you are already logged into cPanel.

In order to use phpMyAdmin without logging into cPanel, you will need a separate phpMyAdmin installation. You can download the installation package from the phpMyAdmin official website.

If you need help with the installation, you can request it to be performed by the SiteGround support team. To do so, log in to your Customer area -> Help Desk - Request Script Installation and post a ticket with your request.