I followed the teardown, now I have an extra piece!

I tried exactly how I understood the steps, but there is only one piece that I haven't found where to attached :(

The piece I am talking about is the little silver square in the image Step 20 located on the top of the battery and on the right of the front part.

It might be the reason the phone didn't switch on after I finished the assembly work.

If anyone can help telling where that piece goes or its function at least, it would be helpful

I also generate this image to make it clear which piece I am talking about: https://drive.google.com/file/d/0B59II8O...