The first method: heat with hot water and flatten the concave part by yourself. Boil a big bucket of hot water first, and then heat the hot water to the concave place with a spoon. After the plastic is heated to a certain degree, push it out on the back of the concave surface by hand until the concave surface part protrudes and recovers. If it feels hard, it still won't come out, which proves that the heating is not in place and requires a lot of hot water to continue heating.
The second method: buy a dent repair kit online. Clean up the concave part first, then put something similar to toilet suction cups in the groove, insert a suction rod on these suction cups and pull the suction rod hard. The principle of this method is that after the sucker touches the metal plate of the groove, the inside is in a vacuum state, and a huge pressure difference will occur inside and outside. At this time, if you pull hard, the metal plate groove will be sucked out. This method needs enough strength, and it needs to be able to find the point of force to have a good effect.