from next time onwards..soon when the baby gets bump..apply cold fermentation..you can use either ice pack or frozen peas wrapped in a hanky..after that you can apply turmeric( take mustard oil heat it little add a teaspoon of turmeric, cool it down at room temperature n apply..)..give arnica (it's a homeopathy medicine for any type of cuts, wounds, etc)..take it under medical supervision..

he is active nothing happens

There really isn't much you can do about the bump except wait for it to subside on its own. At the time of falling you are supposed to first check if baby is conscious, cries well and does not throw up. Next apply an ice pack on the area and compress.