Hi Ben,
I am Dave, I will help you with this.
It is a very bad idea to try to move the full User folder to another drive, there is no direct method to do that safely in Windows, you would need to use syn links in Command prompt to achieve that and many people have been unable to log into that user account after trying to do that, because Windows cannot find the NTUser.dat file to load the profile on startup.
You can move the user library folder like Documents, Pictures, Videos, Downloads... etc. to the other drive safely, but that is all.
How to move over a users Library folders to D:
Open Windows File Explorer
In the right hand pane, right click your Documents folder and choose Properties
Select the Location tab
In the Location box, type D:\Documents then click Apply and OK, you must specify a folder location, not just the D drive.
When that move completes, do the same for Pictures, Videos and Music
Each time, provide a new folder location, for example, Pictures will go to D:\Pictures