A lump over a healed injury is usually due to scar tissue or a small collection under the skin, rather than a fresh clot, and it may take time to settle. You can gently massage the area and keep the skin moisturised, and a warm compress may help improve blood flow and reduce swelling slowly. Avoid pressing or injuring the area again. If the lump is painful, increasing in size, or not improving, consult your doctor for proper advice.