You find the Hotspot on level 2 in the car park right by the exit from the mall. The spaces are marked with GreenMobility signs. There are charging stations on the Hotspot if you wish to charge the car. See how you charge here. If you need a car, that is plugged in see here how to unplug it.
If all the Hotspot spaces are occupied you can park on a vacant space nearby. However, you can NOT park the City Car in the basement, only in the car park above ground which can be accessed 24 hours a day.