cold wash cloth
The best way is to ejaculate. Even if you don't orgasm it will increase blood flow to the penis, and help with treating blue balls.
The pain usually subsides within an hour of the incident. But it can last up to 12 hours in men older than 40.
A not proven treatment is cold water, or something cold on your scrotum. Supposedly the cold brings new warm blood to the area. But it is also possible the the blood vassals will constrict, and make the problem worse.
So either orgasm, or wait. If you do come, your seamen will be watery, so don't be worried if you see that.
Hope you feel better. I would hate to have blue balls.