I hit a pothole and scraped the bottom of my front bumper (not visible from front view). I was wondering if someone can give detailed instructions on how to smooth the scraped painted portion. The scrape is about 4" length by 0.5" width. I am assuming there will be various grades of sand paper involved in the process.

My goal is to have the scraped portion smooth as the rest of the underneath painted portion of the front bumper.