How to insert header ads

HTML header or page layout header?

Pardon, I’m not sure I understand your question. If you go to https://volaretranslations.com, you can see where I have ads in the header. I currently do this via another ad plugin, but would like to consolidate it into one.

This ad is above page layout header.

If your theme has widget position for this place then use widget.
If you theme has special ad space for this position then you can use shortcode.

Otherwise you’ll need to modify theme file and insert call to PHP function adinserter.

https://tinymonitor.com/ad-inserter#manual