Download Android 9 stock firmware for Tanix TX3 Mini TV Box from here or here. Download Android 7.1 stock firmware from here. Download Amlogic USB Burning Tool v2.1.6 from here or download Amlogic Burn_Card_Maker v2.0.2 from here.
Model: Tanix TX3 Mini TV Box
Image file size: 800MB
Platform: Amlogic S905W
Build number: p281-userdebug 9 PPR1.180610.011 20191008 test-keys
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.