Just thought I would let everyone know how I got this to work.
When smartthings detected my 3 gang it showed as a Thing.
I then selected this in the devices and changed the type to IOT8-Z and selected update which then changed the device to have 8 child switches.
Next edit the parent device and change the type back to Zigbee Multi Switch.
This keeps the 8 child switches.
The type will be wrong on the child devices, so you need to select the type Child Switch for the gangs that are on your switch ( Mine was three gang ).
The names and labels should now be changed to something more meaningful and delete the child devices that are not used.
My switches are just Generic Zigbee smart switches purchased from ozsmartthings.com.au
Here is the device 3 Gang Zigbee Smart Switch
