Please note that ResearchGate is not a publisher and not a journal, you cannot "publish" a paper here. It is a platform for papers published in journals, or to present unpublished texts, data etc. See also "Is ResearchGate a publisher?" in https://help.researchgate.net/hc/en-us/articles/14292596164753. See this help page for instructions how to add published or unpublished research to ResearchGate: https://help.researchgate.net/hc/en-us/articles/14293005132305-How-to-add-research.
You should look for a journal in your field of research and submit your paper there. See also the following discussions for recommendations:
https://www.researchgate.net/post/What_are_the_procedures_for_publishing_a_research_paper/1
https://www.researchgate.net/post/For_publishing_article_in_any_journal_which_necessary_steps_should_be_taken_care_by_a_new_researcher/1
