What software should I use to replace an LED display in a train carriage?
I would do this using after effects. You need to do a little bit of motion tracking as there is a tiny bit of motion on the camera as the train moves. Find a font that matches the LED display font on the screen. Carefully match all the colours you use using the eye dropper. Add blur and noise to your comps to better match the footage.
You can fake blurry reflections surprisingly well just by flipping a duplicate of your comp and blurring it. The biggest problem you will have is the swinging handle in the foreground, which you may need to rotoscope with the rotobrush to isolate.
You can see a similar effect (but without any foreground rotoscoping) I made at 26 seconds in here:
https://twitter.com/financialtimes/status/985923651676659713?s=21