It takes time
Did you injure your hand? Swelling can last for a variable period of time depending on if it is broken or sprained and exactly what the injury is.
Between 1-3 weeks would not be unusual. You can apply an ace wrap, apply ice to the area (20 minutes on/20 minutes off), and elevate above heart level to help with the swelling. You will need to have an x-ray done to determine if it is broken.