it's always 'on', you don't need to switch it on or off. But the channel 1 or 2 is selectable only manually by buttons on top. I.e. if channel 1 is selected with button on top, it will not matter if you start playing source 2 - it will still output source 1 even if there is nothing playing on it.

https://www.delock.de/produkt...

It is only mentioned manually.