iPhone microphone not working during call

Hi!

I've having the same problem that was listed here:

Microphone not working when making/receiving calls

It says "What is happening for sure in your case, the second mike near the headphones jack is not working. It seems to be grounded with the body and it's contact is on this particular screw!"

I can't figure out which screw this is. Another tutorial say something about a button under the EMI shield.

Could someone help me with pics of where I can find the screws?