Use the assign command to assign either a mount point or a drive letter.
Also, Diskpart blocks deletion of the partitions that underlie dynamic disks.
Setting FocusMost Diskpart commands operate on a specific target disk, partition, or volume. The targeted object has "focus." Focus simplifies the common configuration task in which you create multiple partitions on the same disk. An object is put into focus by the select command. All Commands except for list, rem, exit, or help require focus.
Commands to Set Focus
Commands to Display Disk Configuration
Diskpart blocks the deletion of the current system, boot, or paging volume. To delete either an ESP, MSR, or a known OEM partition, you must specify the override parameter.