external disk not found

I have an external USB disk which
1/ is detected by Device Manager and flagged as good and healthy (it appears in both disk drives and USB controllers)
2/ I get the familiar “bong” tone when I plug in the USB cable, but
3/ it is not picked up in Disk Management.

Originally, Disk Management found it OK but in my infinite wisdom I clicked on “do not asign a drive letter or path”, and ever since then it doesn’t show up in Disk Management, so I can’t get at it to format it or partition it.
Can I get it back somehow to show up in Disk Management so that I can format it and partition it ?