HDD without drive letter, cannot assign either

I have just migrated from Ubuntu to Windows. I formatted and installed Windows on my SSD. But I had another HDD running for storage when I ran Ubuntu. Now with that drive connected as usual, it's not showing up in Windows. I appears in BIOS and in Disk Management, but without a drive letter. And the option to change the drive letter is grayed out (not available).

Formatting and effectively erasing the drive isn't an option!

What can I do? This is what it looks like:

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