Disassembled display, and I now have a part that is unknown?

Hi, so I had to replace my cousins iPhone 4S screen and I managed to make it alive again, but! There is one contact finger that I wasn't able to put back where it belonged. We had to order a new battery for it as the original short circuited itself (too much force) and therefore I forgot where that specific piece came from. And this time I didn't take any video to have a backup if I couldn't remember something. The pics of the piece are as attachment.

Where does it belong and is it a critical one? I tested the device and I could phone with it and all, but it definitely must have a meaning to it. Any help is very much appreciated!