This article explains how to change the screen orientation of an external monitor when connecting to an M50

When connecting an Android device to an external monitor you must remember that the monitor itself does not have the capability of changing the display orientation. Monitors are considered a "slave-device" and only display whatever signals are sent to it from the computer. So, any display orientation must be accomplished from the computer side. 

Below are steps to enable Portrait mode on an extended monitor connected to an Elo M50 Mobile Computer. 

1. For Portrait Mode to a 2nd Display, Go into the M50’s Android Settings\Display/Advanced/External Screen Orientation, and set it to 90 degree rotation. 

• If you want it to display in Landscape mode set it to 0 degrees.