Do not work on the SmartPlug while powered with 230V. The author accepts no responsibility or liability for any adverse effects. This includes but is not limited to potential damage of the device itself, other equipment or personal harm, injury or dead. Working on electrical mains appliances can be dangerous. 230V is dangerous. If you decide to open such a device and work on it, never plug it into mains, until the device is closed again. If you do not feel comfortable with this, or want to experiment while powered with 230V: Do not proceed!
To program the smartplug, a few wires have to be connected. Only three wires need to be soldered to the JN5168 module. GND and +5V can be taken from the main PCB. Remember the disclaimer. Never work on the smartplug when it is connected to a 230V socket! The following diagrams show how to connect a USB-serial dongle to the smartplug.