It needs to be scraped off with a dental scaler. You can't effectively do this yourself, I would suggest a dental cleaning. I go twice a year for this. If you just ignore it you will get receeding gums due to the constant irritation at the gum line. Dental work can be expensive while a cleaning is cheap prevention. If you are offered a fluoride treatment with the cleaning, just say no.
Daily flossing after the cleaning greatly reduces the tartar buildup.