If you have forgotten your password, you will be able to reset it by clicking on the 'Forgot password' link in the Login screen.
Please make sure that the email address you enter is the original email address with which you registered. Also, you must have access to this email as the reset code will be sent to this email address.
After you login using the reset code, you should set up your new password. You can do so by clicking on the top left hamburger menu and going to Edit Profile at the top of the menu listing. In the prompt for the current password, please enter the reset code you received in the mail.