
Hi @Williams, Stacy ,
Per my understanding, Document Set is a special Content Type. And there is a default content in the Document Set content type. If you set a file here, the file will automatically appear in the new Document set.
However the ones created before will not be updated.
So if possible, I would suggest to rebuild a Document Set content type, add the files you want, and then re-add the document set to the Library you want.
Please refer to this article for more information about default content type:
Configure or customize a Document Set content type
And if the files in Document Set A and B are the same, you can use the copy to function:
And choose your Target site and library:
Please note that using this function can successfully transfer files, but if the columns of the two libraries are different, it may cause the loss of metadata.
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