That looks like the part that goes under the battery connector.
BEFORE you connect the battery connector to the board that piece will go down. There is a hole in that piece, there is also a hole where you took out the screw that holds the battery connector down. Place that piece you have so the holes line up. If you open your iphone and are looking at it with the home button facing towards you of course, take the piece just like you have in the picture grab the little metal part that is facing towards the bottom and just flip it so it is now facing the top. That's how it goes in. So in your picture the little part on the right with the screw hole, it has a little tab facing up. When you put it in the phone that tab will actually face down. It will just sit there until you connect the battery connector. Then put the screw back in. Hard to explain without showing you a pic but at work and cant at moment.
