Great video! Love your outfit, your talking about the food, and seeing you get fuller and rounder as you worked through it. Also loved the low angle at the end, and hearing your burps and how full you seemed. 😊
As to how competitive eaters do it, put simply, they train their stomachs, throats, and jaws to help them consume as much as possible.
The most important one is stomach capacity, which can be accomplished by drinking a large amount of water or other liquid in one go. Start with some goal, say 40 oz., and as that gets easier, bump up to 45 or 50 oz., and so on. Careful not to go too hard on just water though, you don't want to overhydrate yourself!
Exercising your jaw can increase your endurance, and make it easier to get through more food without wearing out your ability to chew. You can train this with gum. You could start with regular chewing gum, but if/when that becomes easy, there's also "Mastic" or hard chewing gum.
Training your throat is probably not quite as important as the stomach and jaw, but it too could certainly become fatigued if you eat/swallow a lot. In a video I watched for research, Joey Chestnut, a competitive eater, says that he trains his throat by doing "burping exercises," which he does by swallowing air quickly (which rapidly works his throat muscles) and then burping it out.
Let me know if I can provide any more info or assistance!