The first is you exhale as long as you can through your nose and then pinch it with a tissue as if you were going to blow your nose. Then keep hold your breath and tilt your head up, then down, then up, then down... Continuously until you absolutely cannot breathe. Then blow your nose and both sides will clear out completely.
The second is to lay down "like one of your french girls" meme, with your head held up in your hand leaning on your elbow. If you are on your left side, the right nostril will clear, and if your on your right side the left nostril will start clearing. This helps get the pressure down.
These work 100% of the time, but for short periods (because of anatomical reasons) but what a relief. Enjoy