This is caused by either the excessive shaking of the head, scratching of the ears or rubbing it against carpet/furniture/etc. Fixing the reason behind the itching is the only thing to permanently get rid of this hematoma. Keeping the dog on a regular once weekly ear cleaning schedule is a good idea afterwards, especially in a labrador that is prone to ear infections.
So first of all, proper cleaning out and treatment of the ear is necessary.
I would definitely clean the ears by using an ear cleaner specifically made for dogs, available from any pet supply store or online catalog or vet. Make sure the canal is filled, then massage the base of the ear well, then allow your dog to shake the excess debris out. Wipe the exterior gunk off. Wash the ears daily, but gently.
You are eventually going to need an antibiotic or anti-fungal from the vet, depending on what the culprit is causing this. The vet will put a sample under the microscope to determine this. The day of your vet exam, don't clean the ears that morning, so some debris will be built up for a good sample.
Until then, continue cleaning daily and do your best to discourage scratching and further irritating the ears. I've included a link here (scroll down) to see how to properly clean the ears in case needed:
An e-collar may be necessary.
When the hematoma is not bothered any longer it may subside on its own. If not or wanting to make sure no permanent disfigurement occurs, it will need a sterile drain placed to disinfect and drain out the bacteria and fluid while healing, which cannot be done at home. If you poke it at home, it's more important than ever to get an antibiotic from your vet. If you haven't poked it, it will have an easier time of healing without infection. You could try squirting some chlorhexiderm or betadine solution diluted with warm water into this hematoma if it does open to disinfect on your own, but results may be variable.
Hope your brother's dog's ear is better in no time. Best of luck,