Download Koobee A660 official stock firmware from the link here and follow the provided flashing instructions to learn how to flash the stock rom.
If you notice that any of the links provided below are broken or don’t work, please post it in the comments section so we can fix and update it ASAP.
Download Options
File Name: Koobee_A660_2.3.6.zip
Size: 202 MB
Android version: 2.3.6
Firmware – Download
How to flash
After downloading the Flashtool firmware, follow the instructions here to flash.