First make sure you plug in your 2.o HDMI high speed cable into the proper HDMI input. Some tvs only have one active HDR input , other tvs have multiple inputs. If you play your 4K ULTRA HDR movie in a same type player ( Samsung , most likely) the player sends the signal out to the 4K HDR capable tv and it automatically recognizes it's HDR. Your tv should also give you a message when it switches on or off HDR. Same location that shows the 3-D icon. You don't need to make any settings change. It's automstic. Look for the HDR icon to come on. I don't know about Game Mode or why you would even choose that to play movies.