Both editions need to be separated from the main work and combined together. You can do this at the same time from the separate menu, or separate them both individually and then combine them. That way the duplicate can be merged into the correct edition. Once the merge goes through, the resulting edition is recombined with the main work.
This edition: https://www.goodreads.com/book/show/1... is a duplicate with no ISBN. Please merge with its complete edition: https://www.goodreads.com/book/show/6...
Thank you in advance.