What and where comes this piece from?

Hello,

On the teardown for Iphone 4, on the first picture Step 6, there is a piece between the two fingers, right hand.

I don't know what it is and where it comes from, where I have to put it. When i dissassembled it (with ifixit tutorials) they don't talk about it and when i finished to disassemble the phone I find the piece but I don't know where it comes from.

If some boby can explain to me ? where I have to replace it ?

Sorry for my poor engligh which is not my language

iPhone 4 Teardown