It's actually simple, but not easy.
Create a calorie deficit
Exercise regularly (cardio)
Have patience and try to constantly lose weight.
Of course, everything is well written in the answer above, but I want to openly rebel: why advise a person to burn fat? THEY DO NOT WORK BY ITSELF. And only in conditions of a calorie deficit and physical activity, which works without any third-party drugs. Even though you burst, even though you burst. But they have a bunch of side effects. Our body does not need to be adjusted and "accelerated", it itself will perfectly cope with the breakdown of fat without you (in the absence of any thyroid diseases, etc.), you just move more actively and eat more modestly.
To get the perfect abs, everything needs to be done with a series of exercises, contrary to the fashionable myth that it cannot be pumped up, that everyone has it and manifests itself when drying, and so on. This is partly true, it is practically impossible to pump it up, that is, to achieve its significant hypertrophy, however, it is necessary to perform exercises to strengthen and achieve a better definition of the abdominal muscles, this is called "spot redaction". Of the exercises, you can single out the leg raise in the hanging on the bar, twisting on the bench, various planks, the most important exercise that you need to do in the morning before meals, or after training is a "vacuum", it will help you flatten your stomach and make your waist a little thinner ... There are also exercises that should not be performed, these are all kinds of exercises for the oblique abdominal muscles. In no case do oblique exercises with weights, this will not make your waist thinner, but rather increase it. This is due to the fact that the oblique abdominal muscles are quite responsive and grow well. Finally, the most important aspect of your workout is not abdominal exercises, but its focus on fat burning, because you will only see your abs when the percentage of subcutaneous fat is low. As for the diet, this is a classic diet for fat burning or a ketogenic diet (which should be used with caution). You can drink L-carnitine or L-carnitine + Q10 complex, these supplements accelerate the basal metabolism and help to achieve better results in losing weight, while not having side effects.