There is usually a pressure regulator in the form of a giant cylinder with a diaphragm and a bike-style air valve that you can pump up. The actual calculation depends on how high the highest radiator in the house is relative to the boiler.
One example of the calculation is here: https://www.slantfin.com/building-height-and-hot-water-system-pressure/ - they are a boiler maker, and this has generally worked well for me.
There is also a bell-shaped automatic water feeder / pressure reducing valve. Most hydronic systems start at around 12PSI cold and go up to 30+ when hot; having the original pressure too high will cause the T&P valve in your system to blow off excess water, and when the system cools down, the water feeder will send more water in. So you'll know that the water pressure is too high if you start seeing water on your floor when the boiler gets hot.
I've never seen the need to touch it myself, though most people do keep them at around 15 PSI.