The first key in doing this is to make sure they have the EXACT same title. Don't name one of them "Ebook Version" for example. If one is called Seeking the Truth - a Medieval Novel make sure the other one has that same title too. The actual title should be the same.
If you make the titles the same, then Amazon will usually auto-match the books together within about a week of both of them being live. I've seen this happen with friends' books. Just be patient, and the books will connect.
However, if you wait a week or two and they just don't seem to be matching up, and you do have matching titles, then it's time to take matters into your own hands.
Here's what you do.
First, go into your Author Central page. If you don't have one yet, it's time to set one up. Here's the details -
Author Central Page on Amazon
It is found at:
Once you have that set up, make sure both versions of the book are on your book list. That way it's crystal clear what books you are talking about.
Now use the feedback button on your Author Central page to send in a request about those books. Ask for them to be tied together.
Note that when you do this your books might "appear and disappear" for a short while in the search listings. That's fine! That is just a sign of Amazon's database going through its updates. Don't panic. Be patient.
After a few days, both should be full live and they should be properly linked to each other!
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