Open your damaged jalousie window to its fullest open position.
Slide the blade of a flat head screwdriver up under the aluminum retaining tabs at one end of the jalousie pane.
Pry the aluminum retaining tab up, holding the pane with your other hand. Pull the tab further out with a pair of pliers, if necessary, to prevent bending it out of shape.
Repeat Steps 2 and 3 on the other side of the same jalousie pane, releasing it from the two aluminum retaining tabs on each side of the pane.
Take the pane to a glazier and purchase a replacement of the same length and width.
Slide the new pane into place and clamp the aluminum retaining tabs down into place with the pliers.