If you previously signed up using an email address and you logged out of ZenSports, you'll need to go to the Email Login page in order to log in again. To get to the login page, first, tap the red "Sign up / Log in via Email" button from the home screen:

Then tap the "Log In" button in the upper right corner of the Sign Up via Email screen:

From there, you'll come to the Log In screen, where you can enter your email address and password. For faster future logging in,  it's recommended that you check the box next to "Save my Login info for next time":