
I don't know if this will help, but I asked ChatGPT AI about your issue and this is the response I got...
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It’s generally not recommended to put a goose’s wing in a sling unless directed by a veterinarian or wildlife rehabilitator. Birds, including geese, have delicate bones, and improper treatment can make the injury worse.
If the goose has a visibly injured wing, the best course of action is to contact a wildlife rehab center or a vet that specializes in birds. They can assess the injury and recommend the proper treatment, which could involve immobilizing the wing in a safe, supportive way or another specific intervention. Avoid handling the bird too much to prevent stress.
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I have raised geese before, but never had to deal with an issue of a bad wing.
We have a local poultry 4H club expert when it comes to birds. He has given me good advice in the past and knows the names and numbers of other people to contact for more information. You might reach out to an organization like that. I would reach out to any good free information first.

We don't have good local vets for poultry. You would get charged $$$ for bad advice. You could probably buy 10 new healthy geese for just one visit to the vet here. Not worth it, IMHO. But I do hope you can get the info you need.
Just found this on YouTube from a wildlife rehab channel...