See these previous discussions:

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

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

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

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

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

Hi,

How about this site:

https://www.grammarly.com/plagiarism-checker?q=plagiarism&utm_source=google&utm_medium=cpc&utm_campaign=11862360200&utm_content=487950086583&utm_term=free%20plagiarism%20software&matchtype=b&placement=&network=g&gclid=CjwKCAjw6fyXBhBgEiwAhhiZskO0Jo9IvNPca83KZVc2L8aFNOYbje6Y_8g-viTUVXG3z1O6_69u7hoCxW8QAvD_BwE&gclsrc=aw.ds

Grammarly is easily available and a very neat service. See some other online tools described as 10 Free Plagiarism Checker Tool for Thesis:

https://www.ilovephd.com/10-free-plagiarism-checker-tool-for-thesis/

https://www.plagscan.com/fr/

https://plagiarismdetector.net