Method 1: Make a paper ball with newspaper, fill the bottle cap, leave it for a day or two before taking it out, and the bottle cap will swell up.

Method 2: When the hat is eight minutes dry, use a hair dryer to blow it out of the hat pocket at low temperature, and the "plastic" hat will also be improved.

Method 3: If all the above methods fail, wet the bottle cap slightly, spread a layer of wet cloth on it, and iron the deformed place through the wet cloth, and the effect is also leverage.