Before hunting for firmware, try a factory reset from recovery mode (Power + Volume Up). If that fails, understand that updating or fixing the ZTE Blade A33 Core via firmware is a high-risk, low-reward endeavor. If the phone is still under warranty, contact ZTE support (though expect little help). If not, consider that the cost of paying someone to flash it might exceed the phone’s current value.
For custom firmware or recoveries, you'll typically need a computer and specific software. Firmware ZTE Blade A33 Core