I am using iPad.
please log out of Todoist, click on the "Forgot your password?" link at the bottom (or, if you go to the full web-app version using this link: http://todoist.com/m/forceRegular , it'll be visible after clicking on the "Log In" button) and follow the on-screen instructions. You'll receive an email with password reset instructions.
If you can't use the Forgot password link directly, type this URL: http://todoist.com/Users/forgotPassword into your browser's address bar.