Change email user values title Ninja Forms.

gistfile1.php

<?php

function nf_change_admin_email_title( $title ) {
    global $ninja_forms_processing;
    if ( 1 == $ninja_forms_processing->get_form_ID() ) {
        $title = 'Here is some stuff';
    }
    return $title;
}
add_filter( 'nf_email_user_values_title', 'nf_change_admin_email_title' );