Note: before proceeding with steps below insert operator's sim card that does not work with device. For example if it's locked to operator "A" insert operator's "B" sim. Check adapters bindings like explained here
Launch DC-Unlocker client
Detect device by selecting ZTE modems from manufacturers drop down menu list, leave Select model as auto detect (recommended) then click magnifying glass button
Wait till program detects device. Detect might not work after first attempt as this device takes time to exit from network adapters to modems/ports. Simply repeat detect when you see installation was completed of MF975 in device manager
Open Server tab, enter your username and password that you received after credits purchase. Click "Check login". (you can buy credits here www.dc-unlocker.com/buy).
If DC-Unlocker/Vygis/Rocker/Infinity dongle is connected, only click " Check login "
How to get user account see here
Open Unlocking tab, click “Unlock” button
Wait for device to be unlocked
After you see that modem was successfully unlocked, restart it by disconnecting and connecting back. Now you can use it with any SIM card.