I am not sure if that is what you mean, but it’s in-campaign DLC. Reload a pre end game save (or whatever the latest save you have and go to your boat. You should get a message to chat with the Steward.
I got the message, that I should talk to the Steward, but my character can't talk to her about the dlc, and he is 20 level
I'm having this same issue. I have tried different saves, I have tried going to different cities, resting in the sea, resting at an inn, etc. and nothing works.
The saves I'm loading are all pre-endgame. My party is lvl 20. Does it matter if I've already played through Beast of Winter?