Screen calibration is done by going into the diagnostics mode:
Turn the audio system on and set it to AM or FM mode
Press and hold the eject button. Then within one second, press the "Seek up" button and hold for about 5 seconds.
The diagnostics will start and do a walk-around speaker test by playing a tone in each speaker. You can cancel that and go into the main diagnostics menu.
There is an option for screen calibration. I haven't done it, but I believe it prompts you to touch the screen in multiple locations to do the calibration.