There is a special sheet metal forming machine. If it is a plastic part, rinse it with hot water and pull it out with the toilet plunger.

The correct way is to let your car "drink boiled water". Boil a pot of hot water, and then pour the hot water into the concave position with a spoon. When the depression is deep, push it out by hand after heating to a certain extent until the protrusion of the depression is restored.