if you use the tissue to clean up the spill you can then interact with more objects to restore them, finally you can click on one of the cracks in the walls to make it open further and let you pass; there you can find the first secret note
there are multiple notes like that one hidden in the game, all of which make parts of the same message about someone being trapped somewhere; the second note is found in the cave below shiptown (entered through the beach) at a point where there is a wall to the right but looks suspiciously like a path, you can walk through the wall and find the note (there is also another entrance further ahead letting you make it into a backtrack), that hidden area turns colorless just like where the first note is; the third note is on a cell in the prison on the fire dungeon, the bars look like they're bent open; the fourth one is further inside the fire dungeon, forgot where exactly, and I've yet to find the fifth (which is most likelly the last looking at all the missing words), but I suspect it's in the island past the rock you gotta push, cause I've yet to push it cuz idk how to push it haha