How can I change a GUI text with a sensor?

Hello,

I would like to know how to change a GUI that is on a vehicle.

What I would like to achieve:

When a train passes a sensor, I want the speed limit to change and the next station to come as text, as well as the speed limit to change.

I have already tried a few things but have not succeeded. if any of you know how to do this please let me know. :D

This can be created with a hit box, a hit box is an invisible part that will trigger the train's message once the train touches it.