Yep, the running board needs to be removed and all that rust needs to be cut out, as explained above. ASAP. Because that open hole is going to let more salty snow get in there and quickly rot out the rest of your trucks rocker. Check the other side too.
I would consider changing how/where the running board mount bracket hooks up. The reason the inner rocker panel is rusted out like it is ...is because the running board mount holds/harbors salty ice and snow. I would recommend cutting off the bracket which swoops *up* ..cut it off and extend metal to the frame, and weld directly to the truck frame. The frame is a lot sturdier and heavier and your running boards won't flex like they used to.
Than get some decent-sized mud flaps behind your front wheels to help keep salty snow from being thrown up under the cab.
If you can't get at it before winter, at LEAST clean around the hole ...and cover the hole with some gorilla tape till spring. Keep salty crud from getting into your rocker panel this winter. And squirt some oil in there too if you get a chance. Otherwise those rocker panels are goiing to disintegrate rapidly.