The best thing to put on a severe burn to help relieve the pain is

cool, running water. Running cool water over the burn can help soothe the pain and reduce swelling. It's important to run the water over the burn for at least 10-15 minutes to ensure that the affected area is adequately cooled. Avoid using ice or very cold water, as this can damage the skin further. After cooling the burn, cover it with a clean, sterile bandage to protect it from infection. If the burn is severe or covers a large area of the body, seek medical attention immediately.