You can't lose fat at a specific area at your body. Just do cardio and it'll go away.
You can tighten the "fat" by doing various lower back exercises if you go to a gym there should be a machine called Hyperextensions (back extension.) Or you can lay flat on your stomach arms straight reaching above your head, lift your legs and arms up as high as you can at the same time without hurting yourself. Hope this helps!
I would do planks in push up postion military press pull ups lat raises deadlifts superman position there are more if u want to lose back fat u need to turn it into muscle if you are not overweight or under weight I would do kickboxing it works core muscle upperbody lower body endurance and stamina and flexibility
Run. Then run some more. Haha
Before I started working out I had that issue with my bra making it look like I had back fat and in the front where my armpits are. And I was very skinny lol. After a few months it disappeared. Pushups were what really helped I think.