You see how they did it in SOMA, but basically you have to create a custom OnGui function and do what you want there.
You can see simpler examples in mods.

a very basic example would be this:
void OnGuiTerminal(const tString&in asEntityName, float afTimeStep)
{

StationGui_TextReaderSingle
(
"Window Title",
"Window Text",
cStationGui_TextReaderSettings(),
cVector3f(0.125, 0.175, 0),
cVector2f(0.75, 0.5)
);

}
after you have this in your script file you use OnGuiTerminal or whatever you call it in the OnGuiFunction in the editor for the terminal.