Out of all the methods I checked on YouTube, this method seems to be the most effective in terms of instantly unblocking your nose.
Basically pinch your nose and sway, until you are almost out of breath, then breath in through your nose. I find it very effective.
This method is very good also: Nasal Septum Mobilization invented by Dr Alan Mandell. It is quite a novel method, so far I have only seen it on his YouTube channel and not anywhere else. I think it may work for people with Deviated Septum as a natural remedy. Basically, the way it works is by moving the septum so as to create a “motion” to unblock the nose.