1. Change password
2. Copy .env.example to ~/.env
3. Edit ~/.env
4. Run install.sh
5. Close Chromium
6. Reboot

Q. It opens open the browser and tries to go to "REPLACE_ME"

You need to edit /lib/systemd/system/kiosk.service and change REPLACE_ME with the real URL.

Run systemctl daemon-reload

Reboot.