Like with original Zynthian, you can connect to a Zynthbox device via any browser from any device that is in the same network as the zynthbox.
To access, type in this adress into the URLbar:
http://zynthian.local
The (default) password is “raspberry”.
Read more information from the original zynthian guide how it works:
https://wiki.zynthian.org/index.php/Configuration_Users_Guide