How can I paste an instance without linking it to old file?

Hi,
While a teammate was organizing 3 different files he copied artboards and pasted them to a single file.

currently all instances linked with 3 different files. When I select an instance there is only one option “Detach instance” but it is not a solution.

so

1. how we can break those links?
2. if there is a way to copy/paste instances without linking them with old documents we can start over and merge those 3 different document’s artboards in single file. Off course after do that we have to create their masters one by one in new document I guess.

thank you