Placeholder text in Widget & Shortcode

I would like to add placeholder text to the email input field in Mad Mimi signup forms (two of which can be seen at https://shemakeswar.com) but am not finding options for this either in the plugin settings in the WP admin or the form settings in my Mad Mimi account.

Is this possible? How can it be done please?

https://www.ads-software.com/plugins/mad-mimi-sign-up-forms/