A. Set the cost to 0. If you want to set free shipping for a particular weight range then you should set the Cost to 0. You should also consider setting the Handling Fee to 0. Here are some unlikely examples.
Note: WooCommerce provides a Shipping Method called Free Shipping which you can use to configure other ways of offering free shipping, such as a minimum order amount or free shipping coupon.
0 | 1.99 | We charge 1.99 for weightless products 5 | 2.99 | Up to 5kg the charge is 2.99 6 | 0 | For some reason, between 5 and 6 kg shipping is free 10 | 3.99 | 7-10 kgs is charged at 3.99 9999 | X | We can't ship above 10kg