Any items that you don't specify as returnable through your Return Groups will not be returnable on the storefront.
For example: you select products A and B as returnable, through a return group called "Returns", but product C is not selected. If a customer were to purchase all three products and wanted to return them, they would be able to return A and B on the storefront, but not C.
Please visit What are return reasons and statuses? for more information.
Bold Returns Manager is no longer available to install on the Shopify App Store. If you already have Bold Returns Manager installed, you will be able to continue using it as it is grandfathered on your store.