This topic was demonstrated on one of the Linus Techtips videos but I cannot find the link. Essentially, from what I understand, the games see the integrated Intel graphics and that is what is used since that is the system default. To override that go to Settings, Display (that should the landing area in System anyway), and at the bottom click on Graphics Settings. It looks as though choosing Universal App from the drop down should then allow you to select the app. Select your game and then click the Add button. From within the game that is now listed click Options and then adjust the graphics specifications appropriately. That should allow your game to use the AMD GPU but have the display sent through the onboard display via the Intel HD embedded GPU.
