The answer to 'how to kill flea' is to use an effective flea treatment product and take steps to eliminate flea infestations in your home. This typically involves treating your pets, washing bedding, and thoroughly cleaning carpets and floors to remove flea eggs and larvae.
For pets, you can use flea collars, topical treatments, or oral medications to kill adult fleas and prevent future infestations. Wash your pet's bedding in hot, soapy water and vacuum carpets, upholstery, and crevices where fleas may hide. You may also need to treat your home with a flea spray or fogger to kill any remaining fleas and eggs. Be sure to follow all product instructions carefully and take proper safety precautions.