If you've passed part or all of the game.
You should go to Gerry (skull), he will ask you to find and dig up the box of cognac. That's the beginning and first quest of the Stranger Sins DLC.
In the beginning.
After the beginning of the game and passing the tutorial, as well as giving away the wine to Gerry (skull). After that, he will ask you to find and dig up the box of cognac. That's the beginning and first quest of the Stranger Sins DLC.