I would say the microphone should be located around the blue circle (its the last picture in the guide):
But how to clean it properly, I cannot help you.
IF you dismanteled everything, and after removing the daughter board from the phone maybe just by using moderate temperatures with a hair dryer could let the chocolate drop out? But could be difficult…
Spare part would only be 5 EUR, so why not give the hair dryer a try?!