Is there any automated way I can detect if a co-author plagiarized before our paper is submitted?

My professor, a co-author and I have been working on a paper for more than a year. I was doing the math and simulations, my co-author was responsible for the writing, and my professor was editing the paper. Now editing of the paper is done. Unfortunately, the co-author is no longer available. My professor called me today and told me he has observed that my co-author copied some sentences from the reference papers. So he asked me to check all of the sentences and highlight and rewrite them again if I found that they were copied. He believes that, these days the reviewers are more concerned about the use of similar sentences in the paper.

So, What should I do? Check all sentences with other papers? This is not possible without using a machine. the paper contains more than 8000 words. Do you know what software I can use to do this?