Need Help with Mic installation on OEM HU

[mister.bond]

Hi from Germany, i hope you can help me .
My friend had a Brand New 2014 Forester XT and he wants a new GPS Headunit !
My luck cause he sold his 2014 Forester XT
OEM Harman Kardon "Head Unit" to me
.....and i installed it in my Subaru BRZ.
So far so good
Every Function runs fine :-)
Then ,i start a Bluetooth Connection with my Phone,
...Head Unit Connects to my Phone....so i thought
it also works.....
So i start a dial up, it connects and i hear a voice from my Dad " Hello ? " he said......
But he CAN´T hear My Voice!!!!!!!!

So i realized my Problem : i have no MIC !!!!!!
so i went to my friend and and he opened
his Forester Doom Light and we found
the OEM Mic.
He cutted the 3 Wires from the OEM MIC and gave it to me.
( he don´t needed anymore cause his NEW Aftermarket Headunit has also new Mic )

So , now, i need Your help please .

Ho can i connect the Mic to the Headunit ????

i Do NOT know anything about to connect that !

please i hope you can help how to do that !