Your WUUM S PRO features reverse charging technology that allows it to function as a portable battery.
To use this feature, you only need to use the USB-C cable that comes with your device and connect it to your WUUM S PRO; on the other end of the USB-C cable, simply connect the device you want to charge.
When you connect your WUUM S PRO to another device that supports this technology, an additional option will appear in the USB Preferences to select whether you want the WUUM S PRO to be the device that is charged or if you want it to function as a portable battery.