So sorry to hear about your duck. If you don't have tube feeding supplies, I would recommend getting them. Sometimes the shock or stress stop ducks from eating and drinking. The injury may also may make it harder for the duck to eat and drink enough. The ducks can heal from some bad injuries, but if they refuse to eat and drink they will die from dehydration instead. Tube feeding can help get them through these challenging times. The supplies can be difficult to find some time, so it is best to look asap.
Here is links on how to tube feed.
https://www.backyardchickens.com/threads/tube-feeding-ducks-updated-5-7-2020.1211994/
https://www.backyardchickens.com/th...ng-guide-pictures-under-construction.1064392/
You can apply bacatracin or triple antiseptic ointment to wound, just make sure it doesn't contain pain relief.
You can also get a antibiotic like enrofloxacin. You don't need a prescription for it. You may not need to treat with it, but it can take time to ship. It is a broad-spectrum antibiotic, so it can used to treat other bacterial ailments.
https://allbirdproducts.com/products/enrofloxacin-10