Well, you haven’t described a problem per-se. That login prompt sounds like the end-point. That’s only used to make changes to the system or update software, etc.
The sprinkler interaction will occur in a web browser on your device (laptop, tablet, phone, etc).
Now you might need the device IP which can be found by typing: ifconfig. This would be done after logging in as you described earlier. The default port is 8080 so the URL would be http://the_ip:8080
Hope this helps.