How to seperate payload_fields into two topic in 'MQTT IN' node

I have already made two signals humidity and light shown in payload_fields in debug message, how can I seperate them into two independent value or two topics? Because after the MQTT IN node, I need to display two signals in the chart which need the real value of the signals.
Another one is I only have one topic now which is /devices//up of ttn, how can I make this topic into /devices//up/humidity or /devices//up/light, because now if I set the topic into /devices//up/humidity,there will be nothing shown in debug window.

Thanks so much!

You can already use the data shown in the screenshot in a chart node by using a change node.
mqtt-in -> change node -> chart node, in the change node use:

add an additional change node and chart node for the light.

Thanks so much! It works!