Windows 10 "Unknown" space on system partition of Windows 10 - 1809

[sa.as]

I used a pc for testing which during the test will be made some restore points. for next test pc will revert back to the first restore point. The problem is after a couple of time of running test my C drive will be full. I had research and found that is related to the restore point but I did not find a solution. I would like to delete these files. I have installed the software(WinDirstat) and you can see there is a huge space of Unknown file ( 110 GB ) which is related to restore point.

I am using SSD on C dirve. I did a disk clean up and delete all restore point but just release 6 GB

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