Hello there, I am happy with telling you about a tool which allows you to use plagiarism checker. It is named Dupli Checker. You can use a  link to it : https://www.duplichecker.com/?utm_campaign=elearningindustry.com&utm_source=%2Ftop-10-free-plagiarism-detection-tools-for-teachers&utm_medium=lin .
In fact, it is very easy to use and it is free. Moreover, it has 2 ways to check for plagiarism. There is a minus in this tool. You are allowed to use the checker only one time if you are unregistered user. To avoid it you can easily register yourself and use it as much as you want.