Is there a way to add a blurb for the backside of my book in scrivener?
How are you getting from Scrivener to a physical book?
Whoever is creating the physical book will have a spec sheet telling you, among other things, what format they want for the cover. Once you have that, you’ll know whether it can be created in Scrivener or (more likely) whether you’ll want to use a dedicated design program. Once you know that, you’ll be able to figure out how to get the “Back Cover Blurb” document in Scrivener’s Binder into the correct location in the “My Book Cover” file that you send to the printer.
Locate it under Back Matter, so that it falls outside of the manuscript’s page numbering and is stored in a logical place when you need to access it.