To access the openstack 's dashboard aka horizon you should try to connect to your controller:/dashboard/ url as mentionned in the official documentation. But ... if you've missed the horizon settings you may have pass through the point WEBROOT :
To modify your settings, you have two options:
Preferred: Add.pysettings snippets to theopenstack_dashboard/local/local_settings.d/directory. Several example files (appended with.example) can be found there. These must start with an underscore, and are evaluated alphabetically, afterlocal_settings.py.
Modify youropenstack_dashboard/local/local_settings.py. There is an file found atopenstack_dashboard/local/local_settings.py.example.
—<cite>https://docs.openstack.org/horizon/train/configuration/settings.html#install-settings</cite>