Download Android ICS 4.0.4 Stock Firmware for ZTE N798+ smartphone from here or here. Download another zte firmware from here.
Archive name: ZTE_N798+_4.0.4_20160317
Archive file size: 232 MB
Model: ZTE N798+ smartphone
Platform: Qualcomm Snapdragon MSM7627A
Build number: msm7627a-user 4.0.4 IMM76I eng.root.20131029.121537 release-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.