Hit top of finger by nail with hammer. Bottom of finger quite swollen and black. Do not think it is broken. What can be done to reduce swelling?

Paperclip. Bend paper clip to have a straight end. Secure with a clamp or pliers so you can hold over a flame until red-hot. Press into the nail until the blood runs out from under the nail. You have a crush injury so it will be sore ; swollen for a few days, longer if the bone was crushed. The black color will gradually be shed off the end in 6 months. The small, round hole will reach the end of the nail so.