“We are aware of a reported issue with the screen display on a very limited number of Galaxy 7 family phones. Anyone who encounters this issue should contact us at 0330-726-7864 (UK) or 1-800-726-7864 (US/International) to obtain a remedy.”
Go to the dial pad on your Samsung Galaxy S7 Edge and enter *#0*# . Then click on Red, Green and Blue. This should reset the individual pixels of each color. If it doesn’t work the first time it might be worth to repeat it several times.
And, it might be or might not help, pressing the top of the screen lightly near the front-facing camera would possibly make the line disappear for a while, according to some users.
Since Samsung hasn’t acknowledged this issue as a widespread one, only the technicians would decide as we have said before, if your device was covered by warranty or the problem is caused by physical damage, which, automatically voids it.