Once the tool displays "Passed" or "Download Finish" , disconnect the cable.
This is the safest method and does not void your warranty or risk "bricking" the device. ZTE Official Website What are the risks of flashing or rooting? - Support - ZTE Firmware ZTE Blade A51
I can give you a more targeted procedure or locate the right firmware file. Once the tool displays "Passed" or "Download Finish"
If your phone is stuck at the logo, use the recovery menu to manually flash the firmware. Firmware ZTE Blade A51
