When I had a hickey before I applied some Peppermint oil to the hickey.
You may notice some tingling but it will eventually go away. Apply the Peppermint oil a few times per day until the Hickey goes away.
It can take a few days to a week for the hickey to fully disappear using the Peppermint oil.
Another option is to apply a cold spoon to the hickey to reduce the swelling.
Although I've never tried it you can also use Apple Cider Vinegar applied to the hickey until it dries 3 times per day until the hickey goes away.
Many people online swear by the use of Apple Cider Vinegar to get rid of hickey's so it's worth a try.