How to partition unallocated hard drive space?

[Windows 10]

I re-installed Windows on one of my computers. The hard drive is 4TB. After Windows installed I see that the C:\drive is only 2TB and there is Unallocated space of 1678TB. When I right click on the unallocated space all options except for Properties and Help are greyed out. How do I create a partition on this unallocated space and format it to use as another partition. I really don't want to start all over and re-install the operating system and all my applications. I would like to use this unallocated space as another partition.

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