How do I disable caching

You can disable caching via WP Admin > Testimonials > Settings > Premium tab and checking "Disable caching?" or likewise via shortcode widget options.

Alternately, in your theme’s functions.php file, add similar code as follows.

add_filter( 'testimonials_widget_disable_cache', function() { return true; } );

or

function my_testimonials_widget_disable_cache() { return true; }
add_filter( 'testimonials_widget_disable_cache', 'my_testimonials_widget_disable_cache' );