You can get to the app on your mobile by going to “Marketplace > SmartApps > More > Multi-Channel Control”
I am also keen on finding a 2 and a 3/4 gang single Z-Wave enabled switch that will work with the SmartThings Hub. I am also keen to find out if the “TZ66D” will work with the official Multi-Channel Control smartapp as I am keen to get one or something similar.
There is another post on the Multi-Channel Control smart app here and here.
EDIT: Dispite appearing to be a double switch, I have found out that the TZ66D only has one switched output, the other switch is to control other Z-Wave enabled devices.
The MCO Z-WAVE Glass Touch Panel Switch 2 Button has two switched outputs and may work with the official Multi-Channel Control smartapp, but I can’t say for sure. It is also rather expensive costing around £70-£80.