Complete the first chapter of each main character's Main Quest storyline to access the exclusive DLC content.

For Andrew's story: Complete Chapter 1 of Andrew's storyline and speak to 22 in Lisbon Shipyard.
For Abdullah's story: Complete Chapter 1 of Abdullah's storyline and speak to 22 in Muscat Shipyard.
For Yun Mu's story: Complete Chapter 1 of Yun Mu's storyline and speak to 22 in Zhangzhou Shipyard.
For Yoshitaka Shizuma's story: Complete Chapter 1 of Yoshitaka Shizuma's storyline and speak to 22 in Nagasaki Shipyard.

More details on the official game page of Adventure of 2233 ...