Many journals ask for a statement mentioning the individual contributions of authors in a multi-author paper. While some journals provide a form or a template for this purpose, others leave it open for authors. You can check online for a contributorship template provided by some other journal. That will give you a fairly good idea of what to cover. Here is one such template that you can have a look at.
Based on the ICMJE guidelines for authorship criteria, what you need to do is clarify how each author has contributed to the paper. You need to create a list assigning a person’s name against the following roles or tasks:
- Conception or design of the work
- Data collection
- Data analysis and interpretation
- Drafting the article
- Critical revision of the article
- Final approval of the version to be published
Note that the names of all the co-authors should be written for the last point. Once you draft the contributorship statement, make sure to get it signed by all the co-authors before you submit it to the journal.