If you have physical access to the player, just flip it over and look for the sticker that has the information labeled serial number.
If you do not, you can do so by going into Zynchro, searching for your player in map view, or by list or filter and once selected, clicking on the Health tab. There you can find the player's serial number. For more detailed information on this step, please refer to the user guide in the Monitoring -> By List section
* The images used in this guide are for illustrative purposes only and designed to be a general representation and/or orientation of the required steps and/ or existing system and are not in any way designed to represent or guarantee aspects of the project, software and or information from any particular unit or location.