Since there is no official Switch port, there is no official way to play Black Flag DLC (such as Freedom Cry starring Adewale) on the console.

If you are looking for the "new" experience on Switch, here is everything you need to know about the DLC and extra features. ⚓ The Rebel Collection Advantage

Originally a PlayStation exclusive, this content is included in the Switch version. It features Aveline de Grandpré, the protagonist of Assassin’s Creed Liberation , in a series of short missions that bridge the gap between the various colonial-era games. 3. The Illustrious Pirates Pack