Note that if you've never set a password, your password is your device ID. If you go to "My Score Profile" (or similar) from a game you can "soft login" and change your password, allowing you to play on multiple machines / multiple games.
If you have a passworded account with an attached email address, but forgot the password, you need to email admin@arc.hiddenade2.io and ask for a password reset! Unfortunately I haven't had time to automate this yet.