Only the authors of publications can upload. However, ResearchGate has cooperations with publishers. Use https://www.researchgate.net/contact to contact them.
As you see two answers and two entirely different viewpoints. I myself categorize broad questions regarding scientific journalism as unanswerable. Of course by which I mean a straight and conclusive answer, but we can share our experience)
The one you asked here, can not have a straight answer. And others are such as peer review, journal policies, editors decisions, just to name a few. The realty is that every single journal decides autonomously.
I can share personal experience of publishers of some of my books and papers. While some even did not sign a contract with me. Some others used to asked me to sign several pages of a contract. Many years went on that I understood that they had clever lawyers, closing all ways for me to claim my published Item. Now even like a software that we use, or the cookies that we accept, just by a click and reading nothing about them, the publishers do the same, we don't read legal pages or rights in instructions to authors, or frequently asked questions, even after acceptance, some journals send pages and ask the author to copy, sign in person, scan and return. Very happy as the paper has been accepted we sign and finished and even if we read, it makes no difference. Sign or not, means publish or not.
Coming back to my reply: As a ResearchGate user, you can create pages for publications only if you include yourself into the list of authors. However, as journal editor you are not an author. Therefore you have to ask the ResearchGate team how to create new entries for all papers published in a journal. There are journal partnerships, see https://help.researchgate.net/hc/en-us/articles/14295063745425-Journal-partnerships. As I understand there have to be an agreement between the publisher and ResearchGate.
Dear Govind Narayan Purohit I would like to rephrase the points made by Wolfgang R. Dick a little bit. What you want is only possible if your/the journal is indexed/listed here on RG.
As asked countless times here on RG, RG is not adding new titles for an unknown period of time, see for related questions: