Note: before proceeding with steps below, set adapter bindings by following instructions here. Also insert operators sim card that does not work with device. For example if it's locked to operator "A" insert operator's "B" sim. Connect device to PC using USB cable
Launch DC-Unlocker client
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 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 E5221 to PC, check these settings here
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. Now you can use it with any SIM card