What are these metal shields and how are they attached?

Hey,

I was doing a Nexus 5X screen replacement and it seems that I have unintentionally ruined the new LCD. A small metal part has become detached from the flex cable.

I connected the LCD to check it and the image went completely haywire. Could it be from this small part?

What does it do? How can I attach it back? There doesn't seem to be any glue involved.