How does the case owner unlock the submarine hotel?

Step 1: Go to the bedroom, check the bed against the wall, remove the pillow and find props: lighters and spoons.

Step 2: Check the bedside table between the two beds and pick up props: wrenches and pins.

Step three, check the book next to the table and find it: a knife.

Step 4, cut the cover of the book with a knife and find it: turn over a few pages of the book with half the note torn, find the other half of the note and put it together.