To reset your password on portal.office.com, go to the login page and click on "Can't access your account?" Select whether it's a work or school account, then follow the prompts. Enter your email address and complete the verification process using the provided security options, such as receiving a code via email or phone. After verification, create a new password by following the password guidelines. Ensure your new password is strong and secure. Once done, you can log in using your new credentials. If you face issues, contact your organization's IT support for assistance.