This depends on the configuration of your clearomiseurs.
You can do it from the top after unscrewing the drip-tip and the top cap of the atomizer. For some models, you just need to slide the top cap.
The charging of the e-liquid can also be reached from the bottom. In this case, you invert the tank and unscrew the base filling.
The payment must be made by the board. Keep the e-cigarette tilted throughout the process to avoid that the liquid reaches the chimney of the tank. At the end, close the ring of airflow. You have to wait for the wicks of resistance soak properly before starting the vape.