Now I have two types of shipping in my store. One is flat rate and other is free shipping. I need a option which will allow customer to replace existing flat rate shipping amount after applying specific coupon (Not all coupons). Suppose my current flat rate is $50 when coupon will be applied then customer flat rate shipping amount will be changed to $30. And it must be a customizable amount. That means a option required into WooCommerce where I am able to input this value.