If you want to just get it done, then you can use a third-party software. It is the easiest way to do it. EaseUS partition master (free trial) is one of many solutions, I use it for such occasions.
To do what you want you first will need to remove the partition (the one with free space) so it becomes an unallocated space (as the one to the left is). To do that -> right click on the partition and click "Remove partition" and confirm. Then you need to choose the system partition (that you're interested in) and then on the bottom of the window by extending it to the side of unassigned space (to the left in your case). Then in the left upper corner you click on the tick icon to apply changes. This will cause a pop-up to show asking to confirm actions (it should be: removal of a partition and resizing of another partition). Applying the changes will require system restart (so as the data can be moved to another sector of the disk). After the work is done, you should end up with something like:
100 MB NTFS system reserved ::: 931.42 GB Win10 (C:)
in your Computer Management console.
Check the screenshot for reference.