Couch is supper saggy.

I'm looking to fix up my parent's couch. They are letting me borrow it until I can buy a good one for myself. I've noticed it's getting increasingly saggy. Makes a pop noise every once in a while when I sit on it. As its been getting increasingly saggy, it's starting to kill my lower back.

I want to give it back to them in a condition better than how I got it. Right now the priority is to fix the saggy issue. It looks like these rods have slipped out of place. I'm guessing that's what the popping noise was? How can I fix this?