Download Android Nougat 7.0 stock firmware PC version for Tanix TX6 TV Box from here or here. Flash it from PC using LiveSuit v1.11 or from SD card using PhoenixCard v3.09. Download previous firmware from here. Download Android Pie 9 stock firmware for Tanix TX6 TV Box from here.
Archive name: 3630847 Tanix TX6 TV Box ROM firmware pack
Archive file size: 718 MB
Platform: Allwinner H6
OS: Android Android Nougat 7.0 stock
Inside archive: firmware + PhoenixSuit_CN + H6¦t-+++-+¦++F
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.