I afraid you will have to replace the LCD panel.
I haven't tried this but, some people have had some success with this (try at your own risk):
There is a way though of repairing a scratched LCD screen though that is inexpensive and very easy. All you need is Vaseline petroleum jelly to fill the scratch on the LCD screen. This very simple remedy works because the optical density of Vaseline more closely matches the LCD face compared to air.
All you need to do is to clean the surface of the screen and then take some Vaseline and fill the scratch with it. Gently wipe off the excess Vaseline taking care not to wipe too forcefully so that you leave some inside the scratch.