Can you wash up the wounds with chlorhexidine, povidone Iodine or saline, then take some photos.
Hard to tell what's hanging out there. Is this a male or female Duck?
Personally, I'd consider culling, but sometimes a bird can recover from terrible wounds.
Keep the tissue moist with triple...
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Is vet care an option? This will be your best course of action to take.
Otherwise, please post clear photos of the wounds and damage, but from your description, likely putting him down will be what is needed.