Hi 
@TMMchickens  Hi Welcome To BYC 
 
Sorry to hear about your duck.
@Amiga is much more knowledgeable about ducks, but I will give it a try
 
Wash the wound with soapy water or flush with saline.  Getting the wound flushed will be helpful.  Apply some triple antibiotic ointment (like plain Neosporin) or Vetericyn.  If there are feathers getting into the wound, you can trim those off a bit.  
I see by the photos you have him(?) separated, that is good.  The biggest concern would be keeping flies out of the wound so they don't lay eggs.  I'm not sure if Swat can be used on ducks , but on chickens it can be applied on the outer edges of a wound to help keep flies out.  But you still need to be vigilant so they don't lay eggs in the wound.  Personally I would not cover a wound like that with anything like a bandage, but others may have better suggestions.
Provide plenty of water - add some vitamins if you have them - keeping hydrated after an attack is important.  Make his normal food available.
Hope all goes well, keep us posted.