Iphone 6 black spots on screen

I have had this black-greenish spot in my iphone 6 screen for a mont now. The spot appeared overnight and still hasnt gone away. The screen had also another smaller black-greenish spot but it went away in 2 weeks. Does someone know what these spots are and how much does it cost to repair the screen? My screen has now be broken for 7 months, I dont know if that has something to do with those spots.