With volcanos, the more viscous the magma, the more energy gets stored before an eruption. Supervolcanos are the most viscous type, hence the massive explosion.

Think boiling water vs thick oatmeal vs boiling a pressure cooker until it explodes, but obviously worse.

So "relieve pressure" in this case isn't like a pressure release valve on a water heater.

You'd need to either cool the mass, remove the overburden, or create some sort of massive voids for expansion.

The US nuclear test done in Mississippi resulted in vaporizing the rock and soil and creating a large underground void, for whatever that's worth as a sort of proof of concept.