1.Wash the area with a car shampoo.
2. Get hold of a 2000 grit sand paper, you can soak it in water for a few mins to soften it.
3. Wet the area with plenty of water.
4. Keeping the sanding paper very straight, gently go over the scratched surface. Make sure your sandpaper is straight. Keep spraying more water as you go. Maintain gentle, equal pressure on a large surface area. Don't dig it in, or apply uneven pressure.
5. When the surface feels smooth to touch, buff it with a 1000-1500 grit compound polish and polishing machine.
6. Finish with a polish.
You will need at least a Dual action polisher or rotary ideally. Hand polishing won't fix 2000 grit sand paper marks. It would take ages. If you can't arrange a polisher then you are better off getting it fixed by a good painter. They can also apply qalam on the bits that don't buff off. Its a 10 mins job for someone who knows what they are doing and have access to tools. You may also take it to a car detailing shop, they can fix it too.