Estabilishing a new database connection in WordPress https://michalzuber.wordpress.com/2017/06/26/multiple-database-connection-in-wordpress/

wp-multiple-database.php

<?php

$wpdb2 = new wpdb('USER', 'PASS', 'DB_NAME', 'HOST');

$sql = "SELECT *
    FROM wp_posts
    WHERE post_type = 'product'
    AND post_status = 'publish'
";
$products = $wpdb2->get_results($sql, ARRAY_A);
foreach ($products as $product) {
    // Do your magic
}

$wpdb2->close();