Black line started to grow from bottom. Retina display.

Sadly there just isn’t anything you can do to fix this without replacing parts. While you can reduce the effect by cleaning out dust from the fans and the heat transfer fins and not cook your system by either environmental heat or running your system hard for long periods of time. Or, use your system on a surface that can block the vents line a bed or rug.

What you are encountering is an overheated T-CON board once it starts showing bars at the bottom or top of the display its fatigued and will need replacing. This is caused by the breakdown of the scanning logic timing so your logic over scans or under scans the sweep that draws the image onto the LCD screen.

LCD’s use a method of scanning to paint the image from the controlling logic. Back in the day with Cathode Ray tubes an electron beam is wiped across the screen to excite the phosphor on it to create white light (like your kitchen florescent light does). Here the beam is very narrow and is controlled by electro magnets! Starting at the top from the left to the right line by line to the bottom of the screen. Here the T-CON logic controls which image cell is lit one by one in a similar manor. But if its timing is off it can prematurely write or end a given scan run which causes these dark lines.

Here’s the needed part: MacBook Pro 13" Retina (Late 2016-2017) Display Assembly and here’s the guide you’ll need to follow MacBook Pro 13" Touch Bar Late 2016 Display Assembly Replacement if you want to fix this permanently.

To prevent this to happen again you’ll need to run a good thermal management tool. I find this one offers the needed features to manage it TG Pro.