The Rebuild Book Indexes button should only be applied if you have books in your collection(s) and you are upgrading to LUNA v7.4.
To Rebuild Book Indexes for a single collection using the Collection Manager, open the Collections tab and select the collection you want to rebuild. Click the Rebuild Book Indexes at the top of the page.
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Next, you will be presented with a dialog box. To continue with the process of rebuilding the Book index click the Refresh button.
