What must existing end users do to set up SMS password reset?

To set up SMS password reset, existing end users must add their mobile number in the settings. This is a crucial step because the mobile number serves as the registration point for receiving SMS messages, which include password reset codes and other critical authentication information. By entering their mobile number, users ensure that the system can send verification codes directly to them, allowing for a secure and efficient password reset process via SMS.

The other options do not facilitate the setup of SMS password reset. Resetting a password using email does not require a mobile number and focuses on email verification instead. Contacting customer support for assistance would not empower users to self-manage their password reset preferences, and logging in as a new user implies creating a new account rather than leveraging an existing one for password recovery. Thus, adding the mobile number stands out as the essential action needed to utilize SMS for password resets effectively.