This code needs to be at the beginning of the HTML generated by the lab:
<!--apertus header start--> <iframe width="100%" scrolling="no" height="42" src="https://www.apertus.org/header?page=lab" frameborder="0"></iframe> <!--apertus header end-->
Which file can it be added to? I had a look at the file structure of phabricator but I am a bit lost still.
Our other websites header bar integration is documented here: https://wiki.apertus.org/index.php?title=Website_Header