A mirror device is not really considered to be a Copy ( this is when using Object Copy), so, you should be able to go to the Device tab, click on the device to highlight, and click on the Change Device button
Now, having said that, I checked the VMware Integration documentation, and it said nothing about devices. Furthermore, I checked the command line options, and the ability to change a device is not even mentioned as an option, so, it may be that it is not possible to restore from a mirrored device when doing a VMware restore
