Re-partitioning, deleting and extending a partition.
One video and a few articles.
Why do you want to do this? It makes it easier to backup the Windows OS frequently and backup the data occasionally.
video: re-partitioning C: drive into a Data drive; deleting and extending partition
https://www.youtube.com/watch?v=pJQ-bm3SY7s
A few articles related to re-partitioning a system drive into data drive
https://www.pcmag.com/how-to/how-to-partition-a-hard-drive
https://www.thewindowsclub.com/re-partition-a-hard-drive-in-windows-10-without-erasing-data
https://www.diskpart.com/tutorials/repartition-hard-drive.html
https://www.lifewire.com/how-to-partition-a-hard-drive-2626081