Im assuming you cant sand it out? You can try using JB Weld to fill it. Then sand and prep as usual. What kind of plastic is it?
Those pieces are more of a fiberglass. I'd use JB Weld. Depending on where it is and the size, you may be able to get away with just filling and sanding it. The gray color of JB Weld is very similar to the natural finish of the fiberglass scoops. Not sure they were painted from the factory
JB Quick will be easier to work with. An actual plastic repair epoxy is best but Quick will work fine