ResearchGate will automatically calculate your h-index when citations will be identified. Note that rather often RG does not find all citations. See these related discussions:

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