Sign into Flood using your Google credentials
After you have signed in to your Google account, you'll be redirected to Flood and prompted with this popup:
If you signed up for Flood with a traditional way (using email and password), but later realised that your email is also a Google email, you can later sign in to Flood using your Google account by clicking the "Login with Google" option on the sign-in page.
Follow the prompt to log in to your Google account. After authenticated, you'll be redirected to Flood.