Bad Drive Letter assigned to a boot driv

In (NT) disk administrator, by mistake I assigned “h:” drive letter to the boot drive. I thought I had selected my other drive. It warned me that the changes will be effective after reboot.
After reboot, it runs a chkdsk and shows that it is running on “h:” drive, then it tries to start and crashes (blue screen.)

How do I restore the drive letter assignment back to “C:”?

Thanks.