See the replies to this similar question: https://www.researchgate.net/post/Journals_not_in_the_list. These may be helpful.

You may also have a look at https://www.researchgate.net/post/Is_it_possible_for_you_to_upload_a_missing_journal_title_to_your_database .

The usual answer given by RG support team is: 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.

thank you, prof. Dick