What will lower blood sugar quickly?

Depends . If you are Insulin dependent, Insulin is the best way. If blood sugars are more chronically elevated then lifestyle change with diet and exercise may address this and maybe also oral diabetes medication. However, if you think you have high blood sugars and you have not seen a doctor for this, you need to do that. Treatment is contingent on your medical evaluation and doctor's recommendations.
Insulin & exercise. Short acting Insulin will lower blood sugar quickly. Aerobic exercise using large muscle groups can lower blood sugar without taking a shot or a pill.