1. Turn off the iphone
2. Release the bolt of the case
3. Place the tool as the image below and pull carefully to open the upper case of the iphone. Unplug the flexible cable connector there.
And now we will see the detail of the home button.
7. After all steps above done, before re-assembling all part try to check the button using the multi tester.
We have tried the steps above and success to repair the home button of the 3gs iphone.