Dead blacklight after screen take apart and reassembly

Hello everyone!

Here's what happen after I take apart the screen to change the camera or change the lighting port I had the same issue with more than 3 iPhone 6 in one row I take the screen apart with all the tools needed I do not understand where is my mistake I'm used to make this king of repair but now I feel that I can not repair anymore without damaging the screen I do it so carefully I repeat the step in my head I do not understand where is my mistake please if someones had the same issue let me know and if there is a fix I would like to know.

The screen work but on the button there is white square sometime big sometime small and that on the 3 last screen I have take apart from 3 different phone 3 different board.

Please any help will be more than helpful so I will not be afraid to do another mistake.

Thanks you all.