You can delete your Shortwave account from the settings section of any Shortwave app.
This will not affect any messages stored in your Gmail account. You can also revoke Shortwave permissions from your Google account. Learn more about how Shortwave takes your security & privacy seriously.
If you choose to try Shortwave in the future, all you have to do is sign up again via Google sign-in. For further questions, reach out to firstname.lastname@example.org