It's easy.
The atmosphere is not 100% toxic. If it would he would be dead.
Cut off 10' of rope.
Tie yourself into a rope harness. retain the surplus rope rope for a french prussick.
Inflate the mattress. That's your supplementary air supply. Break the bamboo pole in half. One half is for a splint. Securely anchor the rope.
Taking the mattress, first aid kit and bandanna with you, climb down.
Stablise and splint the leg.
Apply a touniquet if needed. It may devolve down to his leg or his life.
Tie your french prussik into the rope.
Tie the victim's hands together and get him on your back.
Taking your time, climb up the rope. The french prussick will grip the rope and allow you to rest.
When you get to the top, apply any needed first aid.
Shelter the victim in the tent.
Go for help.