If you are signed into the app, tap on the menu button in the top left and select log out. Otherwise, once signed out there should be a "Forgotten Passsword" button at the bottom of the screen when you run the app. If you tap on that, enter your email address and press confirm, you should get an email with a link to click on. If you click on that link you should be taken to a webpage on server.mensabraintraining.com where you can set a new password. You should be able to use that new password to log into the app again.