Login into the your hosting control panel.

click File manager>>

/public_html/blog (sub domain for which one you install word press)

Here you can see wp-config.php file.

Edit Correct Database Name, username, Password,

// ** MySQL settings ** //

define ('DB_NAME', 'user_blog');   // The name of the database

define('DB_USER', 'user_username');     // Your MySQL username

define('DB_PASSWORD', 'databasepasswod.'); // ...and password

And save the file then try it.