Step 1: Make It Look Like New
Do not use this metod on painted surface, beacuse you can damage paint.
All you need is heat gun. I find some old, but useful heat gun in my garage.
Turn on your heat gun and keep tip of blower 3-4 cm far from surface. Keep on one place until you see difference, and bumper get back to original color.
Take a piece of thick cardboard when you working near painted car surface, and hold it betwen painted surface and blower to protect paint.
I did this today to my car, and it looks preety good.
I hope this will be helpful.