Add new role for specific product when order is completed WooCommerce

functions.php

<?php

/* 
 * 
 *  Add new role for specific product when order is completed WooCommerce
 * 
 * */
add_action( 'woocommerce_order_status_completed', 'ns_change_role_on_purchase' );
function ns_change_role_on_purchase( $order_id ) {
	// get order object and items
	$order = new WC_Order( $order_id );
	$items = $order->get_items();

	$product_id = 3439; // that's a specific product ID

	foreach ( $items as $item ) {

			if( $product_id == $item['product_id'] && $order->user_id ) {
				$user = new WP_User( $order->user_id );

				// Remove role
				$user->remove_role( 'customer' ); 

				// Add role
				$user->add_role( 'subscriber' );
			}

	}
}