I had some similar damage in my roof, when I bought my car. How can you miss such a thing, when buying a car? well, easily..
anyway I used some ultra-fine sanding paper 2000+ roughness and polishing paste. The end result was amazing:
You need some time to rub with this polishing paste to make the lack surface smooth. Low RPM polishing machine with a clean sponge and small amount of paste is excellent.
Disclaimer: Try it first in a less-visible spot. Use sufficient amount of water with sanding paper..