There are several pieces of text that are output on the form that are not specifically related to the fields you add to your form. These are important strings because they provide feedback for those fling out the forms, but on occasion you may want to change those values. For this we offer a simple filter.
Here is an example of all the text that you can actually change using this filter: https://github.com/wpninjas/ninja-forms/blob/48ecae1013fd26e7ad836addc4967b106f45b620/includes/Config/i18nFrontEnd.php
Here is an example of the code you can add to your functions.php file to alter the test:
Note: For WPML support, see the WPML Coding API.
You can also remove the Required Filed Text by adding a space to “FIELDS MARKED WITH AN * ARE REQUIRED” field under Advanced Settings of the form in the builder > Display Settings > Advanced