Basically to adjust you loosen the grub screw near the jaw, then insert the alan key in the hole between 'arc' and 'systeme' and turn to microadjust.
You will need to press the moon against the end of the microadjust screw as you adjust it. When you have it in the correct position lightly lock the grub screw again, don't over tighten.
To get it to click, flip the moon over.