Hidden Partition

In diskpart, a hidden partition reports Id 27 and Type Hidden. Set the ID and assign a drive letter.

Caution: this changes partition type and needs admin rights.

diskpart

Select Disk _
Select Partition _ [1
Detail Partition

Detail Partition reports:

Id = 27
Type = Hidden

Set Id=07 Override

Drive letter

Diskmgmt.msc > Set drive letter