Finding the official firmware for the usually involves checking official support channels or reputable third-party "deep posts" on developer forums. Official Firmware & Support
If you're unable to find the firmware on the official ZTE website, you can try visiting reputable firmware download sites, such as: zte blade a55 firmware link
If your phone is partially working (ADB enabled or rooted), you can dump your own firmware. Use tools like or SP Flash Tool (for MTK) to read the current ROM from your device and save it to your PC. This is the only guaranteed safe ZTE Blade A55 firmware link because it came from your exact device. ZTE Blade A55 (Z2450) Finding the official firmware