Have you bought just the rubber blade insert, or the complete plastic carrier with rubber blade?
Usually we replace just the rubber. With the arm lifted away from the screen, pull the centre of the rubber down, to flex it. This will pull one end out of its little holding legs, then you can slide the whole thing out. Fitting the new one should be a reversal of the removal process. You may need to cut to length, and insert the steel spring strips.
If this doesn't help, you'll need to be specific with the question, or we'll all be confused.