How to access a running application that I cannot see in the regular environment?

I clicked on a game installed in Steam to open.
It opens, but I cannot see it. I know it is opened because when I click on it again, Steam tells me it cannot open because it is running.
I close Steam and try again, but it does the same thing.
I will reboot next.
But if I could just go to that running game then I would not have to turn Steam off or reboot.

Thanks

DPC