wp_enqueue_style specifics for overwriting plugin styles

Put this code in your current active theme function.php file.

function wpdocs_theme_name_scripts() {
    wp_enqueue_style('my-styles',get_template_directory_uri() . '/mystyles.css',array('plugin-style-handle'));
    }
add_action( 'wp_enqueue_scripts', 'wpdocs_theme_name_scripts' );