Unfortunately software will not fix physical damage caused by dropping it.
If this is a screen issue u would need to replace the screen or at the very least take it apart or have it taken apart and the flex cables for the screen to be checked and pushed in firmly, the screens on the air 2 are more expensive unfortunately. As it's one unit with digitizer and LCD.
The old trick of banging it or tapping it on it's back on the left hand side was for the iPad 2 which had a wired connector on that side since them they have a flex which is a bit better which doesn't suffer the same issues.
Unfortunately software will not fix physical damage caused by dropping it.
If this is a screen issue u would need to replace the screen or at the very least take it apart or have it taken apart and the flex cables for the screen to be checked and pushed in firmly, the screens on the air 2 are more expensive unfortunately. As it's one unit with digitizer and LCD.
The old trick of banging it or tapping it on it's back on the left hand side was for the iPad 2 which had a wired connector on that side since them they have a flex which is a bit better which doesn't suffer the same issues.