"Because I once published my article and then deleted it from RG, but my plagiarism related to the article still appears on the researchgate.com website."
Perhaps you removed the article from your profile, but not from ResearchGate in general. To check this, search for the title of the article with https://www.researchgate.net/search.Search.html?query=&type=publication.
In case that you indeed removed it only from your profile, you have to claim your authorship again (see https://explore.researchgate.net/display/support/How+to+add+research). After this you can delete it completely (see https://explore.researchgate.net/display/support/How+to+make+content+private+or+remove+it).