You need to put a file in php
directory called config.inc.php
and it should follow this template
<?php
$database_host = $HOST;
$database_user = $USERNAME ;
$database_pass = $PASSWORD;
$database_name = $db_name;
$conn = new mysqli($database_host, $database_user, $database_pass, $database_name);
if ($conn->connect_error) {
echo("connection error");
die();
}