Go to Start menu and search for Settings. Open the Settings App.
Under the System menu, click on Display.
In this section, drag and drop the monitors labeled with numbers to rearrange each display according to their physical layout on the desktop. Once you're done, click Apply button.
Quick tip: If you're not sure which monitor you're selecting, click the Identify button to figure it out. If one of the monitors isn't showing up, make sure it's receiving power and connected correctly.