Update: As of 06/13, I can confirm that the Tuneskit Audible Converter is able to decrypt Audible audiobooks without using the analog loophole. I set it up on a system without the components necessary to play audio, and the process worked perfectly. It is very quick, and seems to preserve all quality without increasing the file size. Once the files are decrypted, they can be edited using any standard program.
(I cannot confirm whether the software is truly lossless without a control for comparison, but it works more than well enough for me to feel comfortable recommending it. By comparison, software that re-records media is always slow, destructive, finicky, and generally not worth anyone's time.)
Where possible, I still encourage buying from DRM-Free Audiobook stores, so that decryption will not be a problem in the first place. In my experience, Downpour.com and Audiobooksnow.com have a very good combined catalog, as well as competitive membership prices.
My original answer is below...
Unfortunately, there is no software that can edit books purchased from Audible.
Audible audiobooks are heavily DRM'd, and they cannot be decrypted except via exploiting the analog loophole, which is time consuming and reduces audio quality.
(The only semi-exception is when an Audible book is purchased through Apple's iTunes Store—in this case, the book will use Apple's Fairplay DRM instead of Audible's custom solution, and Fairplay can be removed via a program called Requiem.)
In the future, consider purchasing audiobooks from DRM-Free stores such as Downpour.com (Everything is DRM-Free except rentals) or Audiobooksnow.com (most titles are DRM-Free, but check for a "Downloadable" icon before purchasing to make sure).