Precision 3660 - where is COM (serial) port?

Hi,
have brand new Precision 3660 and looking for COM (serial, RS232) port.
Is mentioned in Service manual - Enable or disable the serial port address.
By default, the COM1: Port is configured at 3F8h with IRQ4 option is
enabled.
Workstation has Part No. 3X3PH with i7-13700 CPU and MOBO model P7K8H.
In Win in device manager I see - COM1 with I/O 03F8-03FF on IRQ4 - working normally.

But base question - whrere is this COM port physically?
On backplate is only EMPTY hole prepared for 9pin serial connector.
On MOBO I cant find any header signed COM or RS232.

How (where) can I use it?
Thanks