Woocommerce shipping cost by distance if statement

In woocommerce I use the plugin: WooReer (formerly WooCommerce Shipping Distance Matrix) to calculate the shipping cost by distance. For example the driver have to drive 200 km the cost will be 200 because it cost 1 per km. But I want an function that makes it possible that for example the driver have to drive 300km that I can give you 10% discount on the shipping price. I fount something about woocommerce_shipping_method_add_rate_args but I need help with the code Hope you can help me!