Open the game you want to play on multiple monitors and choose “Video Options” from the main menu. You may need to choose “Options” and then look for “Video” or “Graphics.” Certain games meant for multiple monitors may have a special option on the main menu for setting them up.
Choose a screen resolution for the game that best fits both monitors. If possible, choose a separate resolution for each monitor. If the game allows you to play it across both monitors as one long horizontal desktop, look for a screen resolution that combines the total width of your monitors and has (Wide) at the end. For example, two monitors that are both 1280 x 1024 would use the option 2560 x 1024 (Wide).
Click “OK” to save your settings in your game. Start the game and drag and drop different menus onto different monitors as much as it will allow you. This will vary by game.