HELP!!! Display Issue (Not Optimum Mode)

[pueykia]

Hi, I just bought this game and first time launching it. Each time I launched, my screen will display a box that writes, Not Optimum Mode - Recommended mode 1920x1080 60hz. The screen will go black however I could hear sound running on the background. I already set my screen into 1920x1080 60hz. I am using dual screen, when I unplug the other screen it has the same issue. How can I set the ingame resolution manually? I think it should solve my problem. Thank you!