If you want to do something after WooCommerce order completed then use this code.
woocommerce_order_status_completed action hook is a built-in hook of WooCommerce. It allows you to execute a function as when the order is completed. Add your stuff in inside of my_function().
add_action( 'woocommerce_order_status_completed', 'my_function' );
/*
* Do something after WooCommerce sets an order on completed
*/
function my_function($order_id) {
// order object (optional but handy)
$order = new WC_Order( $order_id );
// do some stuff here
}
Have any doubt, then comment here!