I would recommend talking to your primary care doctor
about this issue, since there are a couple of different possibilities for this swelling that will need to be sorted out by physical examination.
For example, this area of the neck if full of lymph nodes, which can swell in response to infections. Occasionally, an enlarged lymph node can also be a sign of a more serious problem, such as a cancer. Your doctor will be able to determine if this swelling is from a lymph node and, if so, whether it needs to be observed to make sure the swelling goes down or biopsied.
Another common cause of swelling in this part of the body would be some sort of benign tumor under the skin, such as a lipoma or a cyst. Most of the time, these do not need any specific treatment, but they can be removed surgically if they become a cosmetic problem or if they begin to be painful.
Start by booking an appointment with your doctor. They will help you figure out whether you need to do anything else at this time, or just watch the area to see if it changes in any way.