Sometimes it becomes necessary to restore the Windows bootloader if it gets wiped, such as during the installation of another operating system side-by-side. On modern Windows, it’s actually pretty easy to fix things assuming one has a recovery USB or similar.
After you boot into the USB, you hit Shift + F10 to bring up a command prompt.
Next, you need to track down the volume letter. That can be done by using the following commands:
diskpart
list volume
exit
Now you’re ready to run the bootloader restoration command:
Bcdboot <volume>:\Windows
You can now exit the command prompt and then exit the recovery area by clicking the respective X’s to close out and reboot. This should hopefully restore the Windows bootloader.
.