Download Android Pie 9.0 stock firmware for X88 King TV Box from here or here.
Firmware details
Archive name: x88king_20191031_r1
Image: x88king_20191031_r1.img
Archive file size: 640 MB
Model: X88 King TV Box
Platform: AMLogic S922x
System: Android version 9.0
Build number: galilei-userdebug 9 PPR1.180610.011 20191031 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.