You will find recommendations in these previous discussions:

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

https://www.researchgate.net/post/What-is-the-most-powerful-free-plagiarism-checker-software/1

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

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

https://www.researchgate.net/post/What-software-do-you-recommend-for-plagiarism-checking/1

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

https://www.researchgate.net/post/Dear-researchers-Please-i-need-a-plagiarism-checker-Thank-you-so-much/1

https://www.researchgate.net/post/Did-you-have-a-good-plagiarism-checker-like-that-used-in-an-impacted-and-indexed-journals/1

https://www.researchgate.net/post/Which-is-the-best-plagiarism-checker-free-software-or-webpage-for-student/1

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

https://www.researchgate.net/post/As-a-researcher-do-you-think-that-similarity-check-or-plagiarism-check-soft-wares-are-fair-in-all-cases-What-is-your-experience/1

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