How to fix line on lcd

A line on the screen, whether horizontal or vertical, indicates that the connection between the flex cable and the LCD glass for a column or row of pixels has failed. Unfortunately, that kind of damage cannot be repaired, so the only fix is to replace the screen. I wasn't able to locate any iFixit-style written guides, but this YouTube video steps you through the entire process.

How to Replace Oppo A5 CPH2727 Screen — DIY FAST & EASY Repair Guide! - YouTube

So your choice at this point is to decide whether you can live with the line or take the time and expense of replacing the screen. Keep in mind that once one signal fails, there's a good chance more will be coming. It won't hurt your phone any to live with it and you can always replace the screen at any time in the future should it get worse.

Good luck, and be sure to let us know how it turns out!