Which version you are using? Some of the string i do not find. Eg. “Message Box”, “Announcements” etc which you want in h2 tag.

Most string change you will find in templates, So as you are overriding templates in your child theme, you can simply change there.

Sample code:
Add following code in your child theme’s functions.php. This will change message title placeholder

add_filter( 'fep_form_fields', function( $fields ){
    $fields['message_title']['placeholder'] = 'ENter a subject here';
    return $fields;
});

And i charge 50$ per hour.