There are four rules that must be followed to get Kindle for Android (K4A) to "see" books.
- The books must be in an amazon-supported format, such as .mobi, .azw, or .azw3.
- The books must be stored in one of K4A's acceptable folders. The easiest is /kindle. You set up the folders in CC's settings "Formats and folders".
- The books must not be in subfolders of the chosen folder.
- If the books are infested with Amazon's DRM then the book must have been downloaded by the device. You cannot read books that were transferred by Kindle for PC on any device unless you strip the DRM. This is caused by Amazon's choice to use different DRM encryption keys for each device.
If all of these are true, and if K4A is installed, then CC will propose K4A as a reader app and K4A will add the books to its library.
Be sure you have not sometime in the past selected the Overdrive app as the default reader app. If you might have done so, go to CC's settings, scroll to the bottom, and tap "Clear default reader apps".
Note that CC cannot make K4A actually open a book. All it can do is launch the app. You must open the book from K4A's home screen. This is a limitation imposed by Amazon.