I doubt deepstack has this functionality built in, but in the nvidia control panel you can assign specific GPUs to specific processes in Windows. I have had to do that before with some games that were defaulting to the built-in Intel GPU and not using my GTX 1070. I had to go into the nvidia control panel and I forget where it is but you locate the .exe of whatever program/game you want to manually assign and then tell the nvidia control panel you want that exe to launch with the discrete card not the integrated Intel card. I would imagine with dual nvidia cards you can do the same, deepstack's exe is py.exe