I know the charter of the thread is to help you post-process the image you captured, but I want to point out that the noise in the sky isn’t about the ISO, it’s about the amount of light you captured. Without knowing your other parameters, I’d guess you cranked up the ISO to make the shutter speed acceptable (hand-held?), and 1/30sec for instance isn’t really a lot of time for capturing faint light of the night sky.
Decreasing your shutter speed, more light-on-sensor, is the first order of business to clean up the sky. Food-for-thought for your next outing… 