Launch DC-Unlocker client software
Go to server tab, enter username and password, click "Check login". (If you do not have username for DC-Unlocker software, you can buy credits to receive it: www.dc-unlocker.com/buy)
If DC-Unlocker/Vygis/Rocker/Infinity dongle is connected, do not enter username and password, only click "Check login"
Select manufacturer: ZTE modems, model leave Auto detect (recommended). Press detect button (Big magnifying glass)
Wait till DC-Unlocker fully detects modem
If you get "modem not found" error message, run DC-Unlocker as Administrator and perform detection again. Make sure drivers of the device are installed as well - ZTE MF28G Drivers
Open unlock tab and press unlock
Note: if you get Error Connecting to Server or Error Code 62, check Adapter Bindings Settings here
Wait till you see a message that modem is unlocked
After you see that device is successfully unlocked, restart it