Macrium Reflect v6 Problem

I created an image of my wife's hard drive and restored it to a new hard
drive.

I swapped out the old HD and of course it wouldn't boot, so I booted
from the Reflect rescue disk and selected the option to fix windows boot
issues.

No joy.

I selected the view that shows all the HD partitions and I got what I
expected with one exception.

Partition 5, Windows8_OS did not have a drive letter. (Obviously, it has
to be C:.) I ran Macrium's checker and it reported no errors.

How do I assign a drive letter to this partition?

Thanks.