The screen connector ribbon is soldered to the motherboard and not the screen. The screen has the ribbon connectors attached. To replace the ribbon is supposed to be a bit of hassle so if you get one I’d take it to a reputable repair shop who deals with micro soldering unless you are capable yourself. Also is the white line there when the watch is open or closed up or both?. Asking as some batteries aren’t the same size as the old one and even a mm too big could be causing pressure on something when closed up. Had it with a Fitbit once.