Is your TV connected to a cable box? If yes, try switching channels if the line still appears, check cables. Also, do a picture test. If in the picture test and horizontal lines still shows, contact the service center for further diagnosis and if there are any parts need to be repaired or replaced.
My Tv is connected to a cable box from Directv, it’s all white and fuzzy now. No picture at all, I’ve unplugged the cords and did a picture test just stays fuzzy/white. I’ve called LG already so I’m gonna have to take it in and get it repaired. Thank You.