Just to make you aware that there are two plugins - one by Dan Marsden (Plagiarism Trn it in ) which is not going to be supported past 2.7. https://moodle.org/plugins/view.php?plugin=plagiarism_turnitin 

The other one is  developed by Turnitin https://moodle.org/plugins/view.php?plugin=mod_turnitintool - both of these are thrd party plugins so support would be provided by the developers of these plugins and not tested on Totara.

Other plagiarism plugins are listed on https://moodle.org/plugins/browse.php?list=category&id=35