Hi, the file that generates the password field is /administrator/components/com_jsn/helpers/fields/password.php

in XML declaration at line 41 and at line 61 you can try to add hint="enter your password", maybe you will see "enter your password".
I m not sure, because we use simple xml but the field are generated by Joomla API and I have not tested if works.
if not works try with default="password", this will render

But I recommend you to do this with simple javascript
you can put at the end of file /templates/rt_epsilon/js/chart.js this code

jQuery(document).ready(function(){

    jQuery('#jform_password1').attr('placeholder','enter your password');

    jQuery('#jform_password2').attr('placeholder','enter your password');

});