Download Android 9.0 stock firmware for X96 Mini+ TV Box from here or here. Download Amlogic USB Burning Tool v2.0.8 from here or download Amlogic Burn_Card_Maker v2.0.2 from here.
Firmware details
Archive: X96 MINI S905W4
Model: X96 Mini+ TV Box
Image file size: 767 MB
Platform: Amlogic S905W4
Image name: aml_upgrade_package.img
Build number: ampere-userdebug 9 PPR1.180610.011 20190925 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.