To connect to the source database you must add the source database credentials in SP Upgrade options.
All necessary information needed on the options, except from the host, you can find in file configuration.php located at the source Joomla root folder. More specific from there you find the follow:
- public $user = 'username';
- public $password = 'xxxxx';
- public $db = 'dbname';
- var $dbprefix = 'xxx_';
Most of the times people just make typo error so make sure to copy/paste the needed values.
If both sites are on the same server (host), then you on the host field you put localhost. If you try remote connection (e.g. the destination is on your local pc), then on the host you put the IP of the source site.
To find the IP open a dos window and give command:
ping www.yourdomain.com
Also you must make sure that the source db accepts remote connection, since usually host providers do not allow this connection for security reason.
Some of the times host providers give you the ability to open the connection from your cPanel. The IP to give access is the one where destination is located. For example if the destination is installed on your local pc, then google keyword "my ip". For more assistance for this you can get from your host provider.