You need "koreader-kindle-arm-linux-gnueabi-v2015.11-stable.zip" from this page:
https://github.com/koreader/koreader...2015.11-stable
In that ZIP archive, there are two directories:
koreader and
extensions. Did the contents of the extensions directory in the zip file get copied to the extensions directory in the root of your kindle?
It's been awhile since I used koreader but I believe the KPVbooklet simply allows one to open EPUBs and other file types (?) from the home screen.