I did some basic google searching for this solution, and found a lot of old and ridiculous info on how to do this. It’s a very simple solution!
- Connect your device to your computer
- Browse to the kindle folder on the device (typically under root)
- Drag the .mobi file from your computer to the kindle folder on your device
Voila! The Kindle app now has your .mobi file in it’s list.
How To: Add .Mobi Files to the Kindle App on Android