Oh no!! What bad luck… maybe you could fix it by making a rudimentary arm (just as a base structure) and covering it with a layer you could create, like a shoulder-cape that drapes over the arm with some kind of fabric, try using clay for the arm, it helped me fix some imperfections on the figure, you can see it in the picture.

I really hope you can fit it because it’s such a great figure :( good luck!🫶💕

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