Need help to fix an inaccessible USB drive?

I downloaded Macrium Reflect v8 from trusted MajorGeeks and attempted to clone my SSD onto an external USB drive. Now the external USB drive is inaccessible. Grrrrr! Although I assigned the letter M when cloning, Macrium assigned the letter C to volume 0 that I suspect created the problem. Win ChkDsk reports the drive to be healthy. I tried the following without success:

~ Create a simple volume in Windows Disk Mgt (the option is grayed in all four partitions)
~ Macrium's Rescue Media (fails)
~ Paragon Partition Manager (fails)
~ Windows' DiskPart -> list disk -> select disk 1 -> list partition -> select partition 1 -> list volume -> select volume 0 -> assign letter=G. At this point, a notice appears:

"Virtual Disk Service error:
Assigning or removing drive letter on the current boot or pagefile volume is not allowed."

File Explorer does recognize the drive as (G:) and (M:), but neither are accessible (see attached pic).

I searched for software to change the drive letter or to fix an inaccessible drive. All I could find are data recovery tools. But I don't need to recover any data on the inaccessible drive. Is anything else I can try?