Intel Graphics

Hello! I will describe the situation. I have discrete video card (Gtx1070) and integrated in Cpu Iris pro 6200. The monitor connected to integrated iGpu, but every game based on UE4 uses Gtx1070 for rendering, but this card does other things and is not connected to the monitor. (Many other games based on other engines have no same problem). It’s very strange situation, can you suggest solution to the problem please?

Win10x64, i5 5675C, IrisPro 6200 (DX11), Gtx1070, 16Gb 2400 Ram.