To change the Default text error message after the Submit Form please copy the code below and put it into Unbounce LP JavaScript section (bottom in Editor)

 

<script type="text/javascript">
    var d = window.module.lp.form.data;
    /* Please change the main error message TITLE */
   
jQuery(document).ready(function () {
        jQuery('#' + d.errorContainerId).find('.error').text(
            "Change This Title:"
       
);
    });
    /* Please change the individual error messages */
   
d.validationMessages = {
        "email": {
            required: "Oops! Something wrong! Please change ME!!!"
       
}
    };
</script>