First, you have to shrink C. You can do that by using Disk Management.
That will generate "unallocated space". You then need to turn that unallocated space into a logical partition.
You might be able to do that in Disk Management also, I'm not sure.
If not, you can do it with Diskpart or with the Partition Wizard bootable disc.
I'd try disk management and see how far you can get. You can shrink C for sure with that tool, by right clicking C and choosing shrink from the menu.
You'll have to try it to see if you can then turn the unallocated space into a logical partition in Disk Management.
Do not repeat do not repeat do not accept "dynamic partitions". Just say no if you see that choice.