Prerequisites:
You must have a fully running Xiaomi Mi device with Mi account signed in.
Also, ensure your PC has the necessary USB drivers.
Your device should be running the latest official MIUI ROM before proceeding.
Steps:
1: download mi unlock tool
http://miuirom.xiaomi.com/rom/u1106245679/3.5.1128.45/miflash_unlock-en-3.5.1128.45.zip
2:Enable Developer Option by heading to the Settings>About Phone>MIUI.
3:tap 7 time miui version
4:go additional setting> developer option
5: Enable USB Debugging, oem unlocking and bind your Mi account under Mi Unlock Status by heading to Setting
6:Download and Extract the Mi Flash Unlock tool on the PC.
7:Upon extracting, open the MiFlashUnlock.exe file from the folder and click Agree on the disclaimer page.
8:Enter the login details of the same Mi account you logged-in on your device.
9:Now boot the device into the Fastboot/Bootloader mode by pressing and holding the volume keys + Power key for about 10 seconds.
10:After booting into fastboot mode, now connect it to your PC via the USB cable.
The Mi Flash Tool will show the Mi device as successfully connected.
Once connected, then click on the Unlock button.
11:if unsuccessful and show wait 168 hours
Do this after 7 days.