There are NO foods that will "help lose the fat under the belly button."
The only thing that will cause you to lose that particular spot of fat, is OVERALL fat reduction. You lose weight, your body releases the stored fat. But - your body will do so in the order it deems best. If you are one of those that tends to store it there "first" - you'll find it is the last place your body will relinquish it from!
Exercise also will not target the fat stores, but good core-exercises can improve the underlying muscle tone and help you improve your posture, which can improve your overall silhouette.
Sorry, this is not exactly inspiring news - but it is accurate.