What should I do if I returned my device with the iCloud-lock still on? Don't worry, you can remove this remotely! Follow the steps below.
Go to iCloud.com and sign in
Click the Find My app
Click All Devices
Select the device you need to remove
Click Erase the Device (Because the device is not lost, do not enter a phone number or message)
When the device is erased, click Remove from Account
That's it! Your iCloud account has been removed