Your device might have a “default” app selected that is grabbing the EPUB file. You can disable this or select a different default application in the Settings on your Android device.
Or, you can open your Downloads storage folder and tap and hold the file. Then you should be able to select your preferred app.
If you have trouble, you can always read the book in the BookFunnel app. Just tap the book cover in the Library or select Start reading now to get started.