To get rid of crabs or pubic lice use an over-the-counter lotion or anti-lice shampoo on the pubic area where the crabs are.
You can also try soaking the area with Apple Cider Vinegar as Apple Cider Vinegar can kill off lice including pubic lice which is also known as crabs.
Shaving the pubic area to remove the hair where the crabs are hiding can also help because it makes it harder for the crabs to hide.
You could also take a bath and soak in the water and add 1 or 2 cups of Apple Cider Vinegar to the bath water which can help get rid of the crabs as well.
Sometimes you may need to take some tweezers and remove the crabs manually if nothing else is working or go see a doctor to prescribe some strong ointment that will certainly kill the crabs.