EMMC 5.X mode package includes a USB Type A to USB Type A cable "for programming eMMC with vendor tools". How to use it?
Once the eMMC module is installed on your board, you use the top left USB port on the board, and the other end to your PC. Then you use usb burning tool to load the rom/firmware of your choosing.
For the record, usb burning tool is a Windows-based tool used to upgrade (all) devices based on Amlogic processors over USB.
usb burning tool
There is also an experimental tools for Linux https://forum.khadas.com/t/burning-tools-for-linux-pc/1832.
The Le Potato burning tool can be found along with the Android ROM here: http://share.loverpi.com/board/libre-computer-project/libre-computer-board-aml-s905x-cc/image/android/