Click the name of the user account that you want to assign as a device owner.
In the user settings window that opens, click the Devices tab.
Click Add.
From the device list, select the device that you want to assign to the user.
Click OK.
The selected device is added to the list of devices assigned to the user.
You can perform the same operation at DEVICES → MANAGED DEVICES, by clicking the name of the device that you want to assign, and then clicking the Manage device owner link.