To reset your password simply click 'Login' on the top right hand corner of this page. Then click on 'Forgot Password?' under 'I am a returning customer'.
Enter your email address and hit send. You will receive an email with a link in it (please note: this email may take some time to reach you and could appear in your spam / junk folder).
Click on the link in the reset email once you receive it, and you'll be prompted to enter a new password. You can then use the new password to login to your Zalando account.