What I've done last time to slim down to lose weight was to have a good diet plan and stick to the diet plan consistently and be dicipline (can have cheat meal once a week), full body exercise (HIIT + weight training) at least 4-5 times a week, at least 30 minutes per day and do it in 1 session of 30 minutes with minimal rest.

After 1 year, lost at least 10kg of weight (didn't measure fat loss or water loss, but did notice lesser belly fat than before) and wear pants require belts already.

Targeted exercise is only for building muscles of certain parts of body e.g. biceps.

Body fats around ab area are the hardest becoz need to bring down the total body fat percentage close to 10-12% first and then have to follow calorie deficit diet and more cardio + weight training + ab training to bring down more body fat. Then only abs muscles will be more visible as less fat around the ab.

ps: sit up DO NOT help to reduce the fat from tummy/ab and this is scientific proven. Many fitness experts+gurus on youtube mentioned this many times already.