You can’t lose weight in one certain area. You have to lose it all around. So just exercise and eat right, trust me it will work over time. To lose 1 lb a week burn 500 more calories than you eat and double it for 2 lbs.

Your waist is 29-35 inches??
That is a huge difference and not a good approximation.
You don’t need to lose any weight if you weigh 87 lbs, it sounds like you’re underweight, if anything you need to put weight on! You shouldn’t even be worrying about this if you’re 12.

well first of all ur only 12 so u probably wont get such a curvy body yet like tht pic so u probably dont need a smaller waist. and the fat u have is probably just extra skin for when u have a baby or baby fat which u will grow out of.