Saline nasal spray
, it's just salt and water. Some people prefer neti pots which is a device that lets you irrigate your sinus with saline.
Other compounds like menthol can help too. As far as "getting rid" of the cause; it depends on what is causing it. If it's a cold it'll go away on it's own, if it's allergies it'll come back unless you take medicine on a regular basis.