In order to hard reset a ZTE A99, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
ZTE A99 device will be brought back to the default configuration of a brand new device.
1. Power off the device.
2. Now open the dialer. Type in this code: *983*22387#.
3. Lastly, confirm the Factory Rest by selecting Yes.
4. Well done, you have completed the hard reset.