Updating the table of contents

I've updated one of the files - adding a new Heading 1 and some body text.  How do I get the TOC to now recognize this new bit?

To add the new heading to the TOC, right+click the TOC in the book window > Set up TOC. Here you can add the missing format and then update your book. It will add the info to the TOC reference page automatically. You will just need to make it look pretty by setting the font, alignment, tabs, etc.

Further, I poked around to see what you are referring to as "Reference" page for the TOC.  I think this is where you meant:

That's an HTML mapping table—which is an unrelated feature. The TOC reference page is often the last one. Keep paging through until the status bar shows TOC in the center.