They should determine whether the participant has transferred copyright or granted permission for the storage, sharing, and reuse of their work.
If no transfer of copyright has been agreed, participants remain the rights holders of any copyrighted works they create during the project, unless it can be implicitly established that the rights were transferred for the purposes of the project. Because this can be difficult to prove in the event of a dispute, it is recommended to establish a clear, written transfer of rights to the project institution(s), allowing researchers to use and share the research data.
However, transferring copyright does not change authorship: the author always remains the author of their copyrighted work, even when the economic rights have been transferred.