Download Android 6.0 stock firmware for CSA93 TV Box from here.
Model: CSA93 TV Box
Image file size: 596 MB
Platform: Amlogic S912
Image name: aml_s912_q6330-CSA93-20160830_mac.img
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.