Each template is actually a group of files located in a folder named for the template. You need all the files in the specific template folder for the template to work.
/strong-testimonials /templates /default /img config.json content.css content.php
Copy the entire template folder from the plugin into the new "strong-testimonials" folder in your theme. For example, to copy the default template:From
Notice there is no "templates" subfolder in the theme.