Override Single Testimonial Template

I know this has been covered – https://wordpress.org/support/topic/process-to-override-single-template?replies=10

But I am having issues with it – I am using TwentySixteen Theme.

I have copied

/wp-content/plugins/testimonial-rotator/templates/default/single-testimonial.php

to

/wp-content/themes/twentysixteen/content-testimonial.php

And also copied my single.php to single-testimonial.php

But any edits I do to my content-testimonial.php are not used it still pulls from the original template.

https://wordpress.org/plugins/testimonial-rotator/