Do you have a painted grill or chrome? If its painted then it will need to be sanded and repainted. If you have a chrome grill and its startind to flake off there is not a way to fix the chrome besides getting a new grill.
There are a few things that are cheaper than a new grill you could flake off as much of the old chrome and paint it or plastidip it. If you like the chrome look you could try chrome vinyl wrap and wrap the grill. The vinyl wrap wont look like the original but it is better than having the chrome peal off. I used some on the top of the shifter knob its not great but it looks better than having spots if chrome missing.