How can I configure a free shipping discount for all the bundles?

Once inside, check the 'Apply a global discount to all Frequently Bought Together bundles' option and select the 'Free shipping' discount type:

You can configure the minimum bundle amount to apply discounts (zero if you want the discount to apply to all bundles). You can also configure the discount message that will be displayed in the Frequently Bought Together widget, and the discount applied message that will be displayed in the shopping cart when the discount is applied. If you want to configure the styling of these messages, it can be done in the 'Visual styles' section.


Important information
The free shipping discount feature provided by the Shopify Platform is quite loose. You cannot limit it to some particular products or number of products so the only constraint is enforced is the minimum order value.