I am using email notifications in my forms and I would like to add a custom email header in my formidable email notifications.  I created a new template in Wordpress and can insert the templates anywhere using shortcodes such as: [elementor-template id="14975"] I have read this page on the "frm_email_header" formidable hook and read this page on how to use the hook: https://formidableforms.com/knowledgebase/frm_email_header/  I have also read the docs on using the WPCode plugin for creating and using code snippets.  So far so good. Now to the issue: I am not a php programmer and the example in the docs suggest that I should be able to just use this to insert a header:

add_filter('frm_email_header', 'custom_header', 10, 2);
function custom_header($header, $atts) 

However, this doesn't work and re-reading the docs suggests that I need to complete the php function and the above bit of code should look something like this:

add_filter('frm_email_header', 'custom_header', 10, 2);
function custom_header($header, $atts){ ... ? ... }

I have not been able to google or find an example code snippet that would allow for a simple "user this template shortcode as an email header for every email notification".  Can someone point me to what I need to know / read or has an example of something similar that I might be able to modify? And, yeah, I guess it's time that I learn some php.