If you burn calories (exercise), and eat the same calories as before, you are in a calorie deficit. (The same as if you just eaten less).

If you eat exactly as much calories as you need to you can tecnically transform fat to muscles, but its really hard and you need to almost count every nutrient.

Most ppl reduce it too much and risk a rebound. Just eat 50/100 calories less than your daily burn rate and you are on the way. (It’s not really fast, but steady)