Take it off window, the fitting on the right hand side(should be, but check. By looking at the end, if you can see a rectangular metal in the middle opening, its the other end), will need to be unclipped, hold all the rest together, by hand. You should then be able to ease the blind away from the frame, and turn the blind part to increase the tension, keep the blind in the fitting at the end, you dont need a lot of tension, to hold the blind closed, once set refit end piece.
SD, April 2011