Here on RG? If the algorithm didn't detect it in the other reference, there is not much hope for you. You can write to the RG service, but as far as it seems in the feedback from people here on the platform, the success rate there is rather low.

It is not worth writing to the ResearchGate team. All citations are identified automatically, and the team does not have the capacity to add thousands or even millions of missing citations manually. See also these discussions (a small selection from many similar requests):

https://www.researchgate.net/post/Why_citation_score_for_author_publications_looks_different_on_Scopus_research_gate_google_scholar

https://www.researchgate.net/post/Why_are_some_citations_not_visible_on_ResearchGate_and_Google_Scholar

https://www.researchgate.net/post/RG-citations-how-are-they-calculated/1

https://www.researchgate.net/post/missing_citation_number/1

https://www.researchgate.net/post/Why_are_some_of_my_citations_not_shown2/1

https://www.researchgate.net/post/Why_the_citation_is_not_shown/1

https://www.researchgate.net/post/How_can_we_add_citation_on_research_gate/1

https://www.researchgate.net/post/How_add_references/1

https://www.researchgate.net/post/Citations_from_RG/1

https://www.researchgate.net/post/citations_in_RG/1

https://www.researchgate.net/post/How_do_you_fix_missing_citations/1

https://www.researchgate.net/post/How_to_add_missing_citation/1

https://www.researchgate.net/post/What_if_I_have_citations_in_the_research_gate_indexed_papers_that_research_gate_does_not_show_them/1

https://www.researchgate.net/post/Question_about_article_submitted_and_references_does_not_appear/1

https://www.researchgate.net/post/RG_system_to_detected_Citations/1