Change Android HDMI output resolution

Question

I have a screen which only supports one custom resolution(2400x1200), how can I change Android HDMI output resolution to 2400x1200? We can use xrandr on Linux to control parameters of HDMI, but there is no such tool on Android. I googled a lot and got some information such as https://android.stackexchange.com/questions/109343/can-i-set-hdmi-resolution-to-320x240/168396 But my phone doesn't have a mode for resolution 2400x1200. How can I add the corresponding mode to Android system. My phone is rooted and I want to modify some files to achieve my purpose