Self-citation is quiet normal. See these discussions:

https://www.researchgate.net/post/What_is_your_opinion_on_self-citation/1

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

https://www.researchgate.net/post/How_much_self-citations_affect_the_authors_credibility/1

https://www.researchgate.net/post/Is_Self-Citation_considered_as_a_type_of_plagiarism/1

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

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

https://www.researchgate.net/post/Citation-of-own-work/1

https://www.researchgate.net/post/What_are_the_top_journals_attitudes_toward_self-citations/1

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

https://www.researchgate.net/post/Is_self-citation_functioning_in_the_same_way_as_any_cited_reference_appended_to_a_paper/1

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

https://www.researchgate.net/post/What_are_the_dangers_of_self-citations/1

Hello Dr Prof Saeeda Abdullah

Your concerns are reasonable. Sometimes it is regrettable.

https://www.turnitin.com/blog/what-is-self-citation-and-what-does-it-have-to-do-with-academic-integrity

But some would say it is totally legitimate.

https://www.imperial.ac.uk/research-and-innovation/support-for-staff/scholarly-communication/bibliometrics/citation-metrics/self-citations/#:~:text=Self%2Dcitation%20occurs%20in%20an,inflate%20an%20individual%27s%20citation%20count.

I add that it is not only quite normal, as Dr Wolfgang R. Dick said, I highly favour it as it shows you are already an expert in this field.

Thank you Wolfgang R. Dick and Joseph C Lee for providing the links to the discussion. These links were very helpful.