Note: that this process is essentially a factory reset and will cause you to lose some custom information you might have programmed into z-command.

If you lose the admin password to the web interface but still have SSH access to z-command, establish an SSH connection (default credentials are username: pi ; password: raspberry).

Issue the following commands at the console.

cd /home/pi/zcommand
sudo mv z-command.db z-command.db.bak
sudo reboot

Z-Command will then reboot and the web interface should grant you access with username: admin and password: admin.