Q: How should I handle a major revision due to high similarities with my previously published conference abstract?

You can submit a journal manuscript based on a previously published conference paper. However, you need to keep certain points in mind to avoid duplication submission. It seems you were/are not aware of these points. So, we have explained these below. Some of these should also answer your questions.

• A conference paper is a shorter paper discussing only the preliminary findings of a research. Based on the presentation, discussion, and feedback at the conference, you need to build on your research. For the conference, as you have already mentioned, typically only the abstract of the paper is published in the conference proceedings.
• The manuscript you submit to a journal based on your conference paper has to be a more detailed discussion of your research. This should be easy to do because, as mentioned above, you need to build on your research based on the discussions at the conference.
• The content of the manuscript should also be quite distinct from that of the conference paper, especially if the conference paper has been published.
  • As a rule of thumb, the content needs to be about 30% different from that of the conference paper. Again, this should be easy to do because, in the manuscript, you are adding more details about your research.
  • The title of the journal article should also be quite different from that of the conference paper because, if not, there will be two published papers with similar titles, and this is both confusing and unethical.
  • The abstract needs to be different too because it is typically the first information about a paper that is revealed in search results, and here again, if the abstract for both papers is the same, it is confusing and unethical.
• In your manuscript, you need to cite your conference paper, because you are basing the journal article on your conference paper. Additionally, you can mention in the Introduction that the article builds on your conference paper. Perhaps, this is the statement the editor is referring to.
• At the time of submission, you need to check the guidelines for submitting papers based on previously published papers. Additionally, in the cover letter, you need to inform the editor that the article is based on a previous paper. However, in this case, the editor is already aware of this. Nevertheless, you can keep this in mind for future submissions.

If you make the revisions keeping these points in mind, the editor should be fine with your manuscript and should hopefully accept it for publication. All the best!

Related resources:

• Can a conference paper be submitted to a journal?
• Is it acceptable to submit a full conference paper to a journal for publication?
• What are the basic rules for submitting the same research to a conference and a journal?