Launch DC-Unlocker client

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 ".

Note: if you can't login or get error connecting to server after connecting Huawei E5372t to PC, check these settings here

Detect device by selecting Huawei modems from manufacturers drop down menu list, leave Select model as auto detect (recommended) then click magnifying glass button.

Wait till DC-Unlocker fully detects modem

Open Unlocking tab, click “Unlock”

Wait till you see a message that device was unlocked

After you see that device was successfully unlocked, restart it by disconnecting and connecting back. Now you can use it with any SIM card.