Lean down over the sink, with a small pot (a nedi pot is u have one) pour lukewarm salty water in your unblocked nostril. The water will clear out your sinus & should flush out the face paint. It will feel weird, but is actually really good for you.

Your best option is to try and plug the other side of your nose and blow it out. If that doesn’t work you need to go see your doctor, or go to the ER if you have to, and have them get the paint out of your nose.