Epiphan pearl 2 connection

Hi we have pearl 2 on one of our project. Question on which port i need to connect if i want to use rs232 for control, cuz im a little bit confuse why i need usb to rs232 cable.
Im using crestron as control.

The Startech adapter for USB to serial control is specifically for Pearl Mini and the original Pearl hardware platforms. The Pearl-2 has a native serial connection port which eliminates the need for a serial adapter