I've never used an Intensity graph (or chart), but if I look up their Properties, I can find one called Z Scale. So I tried the following:
In a blank VI with an Intensity Graph, drop down an Event Structure on the Block Diagram.
In "Edit Events Handled by this Case", choose "Intensity Graph" (or whatever name you chose).
More choices will appear on the right. The one that looked sensible to me was "Scale Range Change".
As you can see from this picture, the Property "Kind" is an Enum, that takes on three values, X-Scale, Y-Scale, and Z-Scale. "Index" is an I32 number, not sure what it does, but you (who understand Intensity Graphs) can make some changes and see how Index changes (called "Learning LabVIEW as a Scientist, i.e. Do an Experiment"). Finally, "New Range" looks like a Range variable, though I'm not quite sure I know what "Start" means.
Hope this gets you started. If you figure this out, please mark this Reply as a Solution, and also add your own Reply, showing how you actually implemented the Event Structure to "do what you wanted to do", and mark that as a Solution, as well.