how to format my hard drive without a boot disk

Edit BCD to boot only to the new Windows you want to keep.Erase the Old 'D', use it for extra storage or even a memory swap file, or a backup copy of files or whatever, but on the same computer.However, that may still leave pointers and references in the OS itself. Edit the BCD to boot from the current 'D:' but call it 'C:'.Copy everything from the current 'C:' partition to the current 'D:' partition.Erase everything in the current 'D:' partition.

Boot the system from another source, such as installation media.

However, if I had to try, I would consider:

I don't think you can do this with only Windows tools. To make a system partition on Drive 1, you would need to move/resize the Windows Partition to make room for the (new) system partition. In order to boot to Drive 1 you need to establish a system partition on Drive 1, and then set the system to boot from that drive.

Your computer is set to start up from the system partition on Drive 0. In Windows, you boot from the system partition and the system files are on the boot partition.

How to format my hard drive without a boot disk