I was poking around on help, with all the new email templates and found this under Manage your book and series>can I push new content to devices. I have no need to try it, but the last time I used the update categories template they did it in a couple of days.
If you corrected serious errors in your eBook and want us to notify customers of your updates and send them the latest version, you need to contact us. We only send customer updates for serious quality issues.
If you published an updated version of your ebook after you purchased a copy, you can ask Amazon to send you the most recent version.
ASIN/ISBN:
Detailed examples of corrections:
Kindle location number (where in your file is the change):