There is infection in your gums caused by interaction between deposit and bacteria which has given you that swelling Get a cleaning done for your teeth the problem will resolve if not just try laser for that localised area

Ok. In simple language. The area is swollen because of the body's reaction to tartar (one of the possible causes). Tartar is a hard deposit that collects on teeth and needs to be cleaned by a dentist. Other common possible causes for these swellings are hormonal. Visit your dentist for an evaluation. If necessary he will remove the swelling with a small blade. This is known as excision. After excision it is sent to the laboratory for study to determine what it is, from the number of different swellings that can occur in the mouth. Hope this helps.

It looks like localized gingivitis . Cause Tar deposits Treatment  deep cleaning / laser excision