Following the product user guide, simply pop out the inner pod from the silicone strap to access the USB. Connect to any USB port on a computer or wall charger and ensure that the head lamp is plugged in correctly and charging by ensuring that the charge LED's on the front are lit.
If no charge LED's are lit when connected, please try disconnecting and flipping the head lamp over before reconnecting as it could be possible that it is plugged in upside down.