Drill or poke a small hole in the cover, then use a self tapping screw to pull it out.
The APT adjustment screw will be ceased pretty tight in most cases, and can be very difficult to turn or remove.
I recomend making a good fitting screwdriver for it, then heat up the casting around it with a propane torch. Apply some penetrating oil, and see if it will turn. If it doesn't turn easily, heat it up till it starts turning.
The screw is very hard, and the "ears" break off easily if you try to force it....Cliff