Abhishek Kumar

Can you please explain in some detail what is not working for you , and have you added the mail content after installing the plugin please refer the screenshot https://www.ads-software.com/plugins/html-new-user-notification-email/screenshots/

For editing the table you need database access , you must be using application like phpmyadmin from there you can edit the options table check the link here https://wordpress.shadowlantern.com/how-change-wordpress-url-phpmyadmin/ .
Make sure to take database backup first

You have to edit the site_url directly from the database in the options table

Have you tried flushing the permalink. Go to Settings->Permalinks and click save changes which flushes your permalink.

In your mentabox1_rendering function call meatball values by using get_post_meta e.g.;

$features = get_post_meta($page->ID,'room_features',TRUE);

and here<p><textarea style="" cols="90" rows="5" name="room_features" id="room_features" value="<?php //echo $features; ?>"></textarea></p>

remove // ie use
<p><textarea style="" cols="90" rows="5" name="room_features" id="room_features" value="<?php echo $features; ?>"></textarea></p>