In general you can merge files by right-clicking in the book browser on the file(s) to merge and selecting 'merge'. If you only select one html file it will merge with the file directly above it in the book browser.
In your case that wouldn't help very much.
I'm assuming each <h1> has a unique title...?? If so, I think you will need to manually copy/paste the <h1> tag from the list to the individual html files.
If the <h1>s are a simple list of chapter numbers then you can use the
ReworkChapteHeads plugin to add chapter headers to each page.