There’s the “quick” word again. Changing your body…it takes what it takes. And it’s rarely quick. If you gained 100 pounds of weight over 4 years, then it is reasonable to think it will take 4 years to lose it. Of course, you can gain it or lose it faster. However, radical change is rarely sustainable. Think of everyone you know. How many have changed radically and sustained it? If they did so, I bet something cathartic occurred that inspired them to change their life. Otherwise, fall in love with the process and be proud of your journey along the way. You’ll get there when you get there.
But let’s at least answer the question. Six-pack abs quickly? Ring all the water out of your system, and there they are.
What is typically required? Roughly, 6-13% body fat. It varies between, age, sex, muscle mass, etc. Genetics also play a large role. The question is, “why do you want that?” Usually, people like the way it looks; they feel attractive; it’s a benchmark for success. The “how” requires restricting your calories for enough time until you are lean enough that your body composition is within the 6-13% range. Then if you want larger ab muscles that “pop” when seen, then you must make your ab muscle grow. How do you do that? Add resistant training to your core work. Make your core work heavy, and then your muscles will grow. Combine the nutrition restriction with heavy ab work, and then you’ll have a bit more of what you want.
Note, a visual 6-pack does NOT mean the abs are strong. It simply means that you are lean. If you want a strong core, then do things like heavy squats, dead lifts, isometric holds, unbalanced carries, and then you will have a stronger core. Then you will be better protected for what you’re trying to do in life.