You can't figure out where to connect it, because it's the wrong EHS cable. It won't work at all with that phone.
That cable is for the Poly VVX series phones.
There is no longer a EHS cable being sold for the OBi 2xxx series, which are EOL. There's no support for that phone. Send it and the cable back to wherever you bought it.
If you want a current-production Poly IP desk phone, get one of the VVX series, or the Edge B series.