i™ve read online that your derm can prescribe ointments to help like hydroquinone, but from what most people say is to just let them fade away by themselves. it can take anywhere from a month up until a year but thats only for really severe hyper pigmentation. 
yours seems to be mild so it shouldnt take long at all. just remember to always always wear a suncream with a high spf to stop them from getting darker or leaving behind permanent spots!