How should I get rid of the blood blister on my belly button piercing?

Please see your doctor immediately. You could end up with a bad infection. In the meantime, buy a large bottle of Hydrogen Peroxide & pour it over the site three times daily, until you can see your doctor. The treatment, will keep the area cleaned good. Blood blisters should NEVER be squeezed or punctured. Just leave it alone. Don't get anymore piercings, if you're not going to keep them cleaned on a regular basis. Not doing so, is only asking for more trouble. See the doctor, soon!!!!