Uninstall, you can't.

---

On March 21st 2024: "We’re inviting you to try the game before the official release! Starting today, the free prologue of Age of Water — The First Voyage — is now available. Welcome to your first voyage! Load your machine guns and cannons, and get ready for fierce battles and amazing discoveries.

More good news! All progress from your adventures will be saved and you’ll be able to continue your journey from the same point in the full version of Age of Water. Remember that the prologue is only the first adventure, and that there’s a huge water world ahead of you, the secrets of which you’ll have to uncover.

The full version of the game will become available on Steam on April 18th!"

On April 25th the full game was released. It appears that on or around this date, the 'free prologue' was removed from Steam. So you could play this 'free prologue' for a total of around 36 days.

So this game was a bit of a scam. I have a life and left it installed for a time when I could play it, which happened to be a few months after it was removed from Steam. So I never tried this 'free prologue' and I never will. Game has quite a high price tag for something with no demo. I won't be buying it.