The 1st way is very easy: you just need to place pressure on a point above the nose bridge. The bone in this area will start swinging and it will stimulate the flow of fluid.

The 2nd way requires holding your breath: pinch your nose, hold your breath, and start nodding your head. These movements will cause carbon dioxide accumulation and your brain will flush the nose sinuses because of the lack of oxygen. Then you should be able to blow your nose.