I'm facing this problem too. For the last few months, I've gained a lot of weight and that is visible from my face too.
But for me dieting and exercise work very well. I remember I had this same issue 4 to 5 years back, when I gained a lot of weight, but when I controlled my diet and did some sort of exercise (but mainly dieting, coz didn't get enough time to exercise), I was able to reduce my weight and make my face slimmer.
I'll do the same now.