To Zineb Lamghari: The usual answers given by RG support team are:
If your journal isn't visible in the drop-down menu, it's not in our database. We're not currently adding journals to our database by request, but this may change in the future.
We're currently making improvements to our journal database, and in the meantime, we're not adding any new titles. Thanks for your patience.
When a journal is missing in RG's database, I add the bibliographic data to the abstract field (like, e.g., in https://www.researchgate.net/publication/268925009).