[Plugin: Visual Form Builder] form_success_message

I like to customize the form_success_message, so I edited the file visual-form-builder.php, but it still prints the old text. Where else should I edit?

<?php
                                                    /* If there's no text message, make sure there is something displayed by setting a default */
                                                    if ( $form_success_message === '' )
                                                        $default_text = sprintf( '<p id="form_success">%s</p>', __( 'Thank you for your information, please download Surgimap Spine from below.' , 'visual-form-builder') );
                                                    ?>

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