The output screen is directly to the right of the Interface, and in Dual mode the second output is directly to the right of the first output.
The previews for the buses and screens can be found top centre of the interface.
This is a screen shot showing the Single Output Mode, with the A/B crossfader below its preview area.
Also shown here is the crossfader, which mixes between the A (left) and B (right) Buses, there are also some auto crossfade controls under this. The speed of the auto fade is based on the current TX Speed setting.
And this is a screen shot showing the Dual Output mode, notice each output has its own A/B crossfader and auto controls.
The button between the outputs locks the crossfaders together. With the crossfaders unlocked you can control the Bus mix separately for each output.
The management of the outputs can be found via the 'Configuration & Tools' tab,
and accessed via the 'Configuration' button. This will pop-up some basic application setup options.