I am looking at the amount of pin feathers- to actual feather ratio- seems a bit strange, is threre some crazy molt? (could be a underlying condition that made the bird suspetible).
For chickens with wounds, the safest and easiest option is diluted Betadine (povidone-iodine) or a hypochlorous-acid spray like Vetericyn. Both disinfect gently without stinging or harming tissue, and they help prevent infection while allowing the wound to breathe. Start by flushing the area with clean water or saline to remove dirt, then dab or spray with diluted Betadine (tea-colored, not dark brown) or Vetericyn, and let it air dry. Personally I avoid chlorhexidine āit can irritate some birdsā skin profoundly and definitely not good for open wounds on chickens (mammals is questionable per amount and weight). Harsh products like hydrogen peroxide, alcohol, or anything with ā-caineā pain relievers (like neosporin with pain relief), as those can burn tissue or poison birds.
Apply, once or twice a day until the wound heals, and separate the bird if others might peck at the injury. I am concerned wiht the images however, something seems amiss- especially around the vent.
What do you think the attack was?
(feline requires antibiotics).