The most common cause of duplicates in your read or to-read list is a duplicated Goodreads import. We always recommend wiping your StoryGraph account before you upload a new Goodreads import. This can be done by going to Manage Account in the top right corner menu, then using the 'Delete Owned Books' and 'Delete Books, Reviews & Tags' links.
Once your account is empty, you can then upload the latest version of your Goodreads data without the risk of duplicates.
Please note that we do display rereads as separate entries in your read list. If you've read a book three times, it will show up three separate times in your read list.
If you only have a few duplicates, you can delete them using the 'View/Edit Read History' button on the book page. In the app, this is behind the three-dot menu:
In this view, you should see your two read instances listed like this:
Use one of the little x's to delete the spare read instance.
If you're still having trouble with duplicates, please send us an email at support@thestorygraph.com!