Manually Editing header.php
You can add a Divi Builder layout to the header of your pages by editing the header.php file in Divi (or better yet, in a copy of the header.php file placed in a child theme).
To do so, replace this line in header.php:
<div id="page-container"<?php echo $page_container_style; ?>>
<div id="page-container"<?php echo $page_container_style; ?>> <?php echo do_shortcode('[et_pb_section global_module="5944"][/et_pb_section]'); ?>
Note that if you have edited the Divi files directly, then your changes will be written by future updates to Divi and will need to be re-applied. This should not happen if you edited a copy of header.php in your child theme, but note that changes Divi makes to its own header.php file won't be transferred across to your child theme header.php and so you'd need to manually repeat your steps if you want to take advantage of any enhancements Divi makes to its own header.php file.
Using a Plugin
There are a couple of plugins for Divi which allow you to add Divi Builder layouts across your sites, in various places such as above and below the main header. These are:
The main advantage over these plugins, apart from being easier to use and requiring no coding, is that they should not be affected by Divi updates.