OK, my bad. As this was listed on the "e-reader" category I thought you were talking about the regular Kobo reader.
I apologize. Please follow the steps below from the Kobo VOX:
1- Tap the Home button on your Kobo Vox
2- Tap "All Apps"
3- Tap the "Get Apps" icon
4- Tap the white search bar near the top of the screen and enter the name of an app. (Here enter the word kindle
5- Then when you see the Kindle app listed, tap it
6- Tap Download. The download will begin automatically
7- Open Notifications by swiping downwards from the top of the screen
8- Wait till the app has downloaded before completing the next step
9- Tap the app. The app installation options display.
10- Tap Install
More info clicking here -----> http://goo.gl/GSA6r
If you would like any additional information or have more questions please don't hesitate to ask!
Please remember to press the ACCEPT button when we are finished, it is the only way I can get credit for helping you. I want you to be 100% satisfied so please, by all means ask any questions you might have on this subject. Positive feedback is always appreciated.