I have big cheeks since when I was kid, How do I reduce them as they make my face so big, I already reduced in weight, and does chewing gum help?

See plastic surgeon. This problem can be easily improved by a buccal lipectomy. See plastic surgeon for evaluation and treatment options.
Chewing gum. No, chewing gum will not help. To change the shape and contours of your face requires the services of a highly skilled Plastic Surgeon.
Big Cheek. Usually with age the buccal pad of fad starts reducing and cheek is not so bulky in appearance. If you are young , your fatty cheek will reduce gradually and you do not have to do anything otherwise consult a plastic surgeon..