Can I configure my shipping rates using Shipping Rates Calculator+?
Shipping Rates Calculator+ displays your shipping rates exactly as they are configured in your Shopify admin.
The app cannot be used to configure shipping rates, only to display them. The shipping rates have to be configured in advance in your Shopify admin.
You can find all the information regarding shipping rates configuration on the Shopify Shipping Tutorial at https://help.shopify.com/manual/shipping
https://apps.shopify.com/categories/shipping, many of them feature different ways to configure shipping rates.