There are 2 wires at the switch, one with power and the other goes to the outlet.
Join your new wire to that switch wire with a short pigtail that goes to the switch.
The whites (neutral) will be in the back of the box, just add your white to that.
Join your new wire to that switch wire with a short pigtail that goes to the switch.
The whites (neutral) will be in the back of the box, just add your white to that.