cannot find your Theme Editor section

Hello,

The most easy way is to add it using a free plugin: https://wordpress.org/plugins/insert-headers-and-footers/

If you want to edit the header.php file directly then you need to copy the header.php file from the Parent theme to the Child theme and then try adding the code in it.

Regarding knowing how you can set up Child Theme, please check out the following guide: https://xtemos.com/docs-topic/setup-child-theme/

Further, regarding the main concern you can read the following Article for further help:
https://www.wpbeginner.com/plugins/how-to-add-header-and-footer-code-in-wordpress/

Hope this helps !

Best Regards

Hello,

The Child Themes are basically used on the Site when you want to do the custom code changes at the Theme files level so that the changes won’t get wiped out when you update the Theme (if update gets released of the Theme).

So, if you have done any Theme file level change in your Parent Theme then you need to do that change in the Child Theme and remove it from your Parent Theme because when you update the Theme (which would certainly be Parent one), the Theme file level changes will get wipe out.

Hope we have cleared your doubts now.

Further, you can read more about it here on the following Articles, if they are of any help:

https://developer.wordpress.org/themes/advanced-topics/child-themes/
https://www.wpbeginner.com/glossary/child-theme/

Best Regards