Can you explain how do we decrease swelling of the salivary gland?

Depends: It is not normal to have swollen salivary glands. Some could be serious, so it is best to find out why you are having this issue before how to deal with it. Remember, diagnosis first before you find the right treatment. Even with a benign salivary stone, the gland can get infected secondarily. So visit a dentist and find the cause first.