If Free Shipping is available, you possibly don’t want to show the other paid shipping options. WooCommerce shows by default all shipping rates that match a given shipping zone, so it’s not possible to achieve this from the settings alone.
You need PHP for that. In this example, we will disable all shipping methods but “Free Shipping” so that free shipping remains the only possible choice. And here’s the code to add to your functions.php
PHP Snippet #1: Unset Specific Shipping Rate When Free Shipping rate is available