good advice to use pin or paper clip, and I have had a bit of dirt stuck in the jet which caused it to direct the spray way off target.
By the way, I got so fed up of my rear screen jet dumping most of the washer fluid vertically straight down the screen and onto the rear bumper that I turned the spray head 45 degrees from its normal straight down position, it then sprays across the screen and more of the fluid actually gets caught by wiper blade and does what it is supposed to do - clean the screen and not the bumper. It may turn without slackening the lock-nut, but its easy to get to anyway.