It's actually not that hard, put the index and middle finger on the top part and push against the bottom part with your thumb. Literally takes less than a second.
Finally. They will get together this volume (or I'm mistaking the chapter titles)
Considering the name of the previous chapters in the past volume, it could all be a trap until the author decide to end the manga, or get axed prematurely.
I feel kind of bad that nobody bothered telling her that she had that note on her back, but then again, maybe they read what the note said and decided it was best to leave it there.