I would agree with Geek-9pm.
Only if it is critical for you to keep your data from Kali, just load Windows on your machine and then reinstall Kali after that. If you must, read on.
Microsoft OS's depend on being the primary OS on the drive in order to boot. Linux too, it could be argued.
Booting multiple OS's is a feature enabled by GRUB, which is installed along with most (If not every) linux distribution. GRUB is like it's own mini-OS that loads from the primary partition and, once loaded, can boot up any other operating system on any other partition.
The linux installation, if Windows is installed first, will take care of configuring GRUB to have an option to boot into that.
If Windows is installed after, you'd have to either try running update-grub
from Kali and seeing if it will detect windows, or manually edit your GRUB configuration.
Personally when I had this issue, I just backed up my data, installed Windows on the drive, then did the linux install and let it autoconfigure GRUB for me.
Let us know what route you take. I hope you get this worked out.