Instructions
Play through the game until you reach Chapter 4, after you have completed the Day 3 quest in Rivet Ravine and obtained your Level 4 License. When you reach Chapter 4, you will find that Bottomsup Bay has been unlocked.
Speak with the woman at the desk outside your home and she will ask which dig site you want to visit. Pick "Bottomsup Bay," and you will travel there automatically.
Watch the short cutscene once you arrive at Bottomsup Bay, then save Rosie from the Denture Sharks. Walk west, and you will find a large rock near some coral. Smash it to reveal a hidden passage. Enter it.
Walk straight ahead to find Woolbeard's sunken pirate ship. Go inside and head to the left, past the first set of stairs, then go up the second set of stairs to the second floor. Walk down to the end of the hallway, past the set of stairs leading to the third floor, and you will find a room.
Go into the room and open the chest to get a book that teaches you how to use Team Skills. Holt will appear and explain how they work.