See this help page for instructions: https://help.researchgate.net/hc/en-us/articles/14293005132305-How-to-add-research. Before adding data manually, you may check whether some or even all of your missing or new publications are already in ResearchGate. In this case you need just to confirm your authorship. Open https://www.researchgate.net/profile/Satoru-Hashimoto-4/unconfirmed (visible only to you). In addition, you may search for titles of missing publications at https://www.researchgate.net/search.Search.html?query=&type=publication.