I'm very sorry to hear to hear that...
From your description, it really seems that your budgie was the victim of bad fighting and it would be good to inspect the budgies on your aviary in order to try to find the culprit(s) and then isolate these budgies.
You can find clues on the attackers by checking blood stains on the beak and on the cheek feathers.
As for your injured budgie, if you can't take him to an emergency clinic then you can provide first aid, by cleaning the wound on the wing (you can wash the area with sterile saline solution) and then applying Betadine to disinfect the wound.
Keep the cage warm, by covering it on 3 sides with a blanket. If need be, place a hot water bottle underneath the cage's bottom for extra warmth.
In order to reduce the stress levels, having some background noise from the radio or TV would be good.
As for food, you can offer your budgie some egg food, this is highly nutritious and can be quite helpful in nursing sick and convalescent birds.
Soaking some millet spray in electrolyte solution will also be a good option.
You can find more detailed information on this by checking this link: https://talkbudgies.com/your-budgies-...te-recipe.html
I'm wishing your budgie a steady and full recovery.