Well, if you had extensive numbers of non-OS files that had been stored on C: that have now been moved to D: your problem may already be solved without doing anything further.
Open File Explorer and click on "This PC" then take a look at what's shown as far as how much space you have on each of your logical drives (which correspond to the partitions). None should be showing the "amount of space taken" bar in red.
I always like to have about 25% free space, at a minimum, on the OS drive, and if you don't, and the partition for D: is next to the partition for C: and it's nowhere near to full, I'd expand the C: partition such that it takes some of the D: partition's space. The partition manager takes care of moving the actual data in D: as needed to accomplish this.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
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~ Lauren Bacall