Get Calibre for the Kindle.

Get this Kindle plugin zip file.

Unzip the file, Open Calibre>Preferences>Plugins>From File>Unziplocation/Calibre_Plugins/

Choose the zip file

Customize plugin>Enter the Amazon Serial No

The serial no is located from Kindle>Home>Settings>Device Info>Serial No “B00E-” (example)

Hit Ok, close and restart Calibre.

The DRM is removed while importing the book to Calibre. So if you’ve already added the book, delete it from Calibre and readd it.