I don't have Tome, so I can't give any real help and you've probably done all ths before. But I'll through out a few suggestions anyway, just to help you waste time looking.
Look for any settings in the app. Usually it will be a gear shaped icon.
Look for the DropBox option in your libary, import, and export options. No matter which, try it and see if it takes you to a DropBox logon.
Check under the iPad's Settings app. Scroll down the apps and see if Tome is there and what settings are available.
That's it. Hopefully someone who uses the app will wander in and give you better advice.