Your Lunewick online save is kept on our own server. Deleting it there takes a minute: type the email address you kept your save with, then the 6-digit code we send to it.
This deletes your online save, its backup and your email address at once, and cannot be undone. The game on any phone keeps working, starting fresh. Purchases are recorded by Google Play, not by us, and are not affected. You can also delete everything in the game: Settings, then Delete my data.