If you want to tighten your abdomen, you must first make sure that your body fat content does not exceed the standard. If it exceeds the standard, then lose weight first. Slightly exceeding the standard can directly reduce fat, and seriously exceeding the standard must first lose weight. As for abdominal muscle training, most of the abdominal muscle training intensity can't reach the function of quickly depicting abdominal lines, even if it is done many times, it is useless. The key is to adjust the diet.

If you want me to give more detailed advice, you'd better tell me your gender, age, height, weight and target weight. Tell me the existing fat content if you know it.