Use the Download tool now in this article
https://www.microsoft.com/en-gb/software-download/windows10 and you can create the latest Win 10 ISO boot disk for your system and then perform a repair install.
When you get the choice of USB or ISO - choose ISO and after it has downloaded and saved to your Docs folder you will be prompted to open DVD burner - stick a DVD in then click Next to point to the Windows image.
The download is ~3.09GB so can take some time depending upon your download speed.
Open Windows Explorer - This PC - stick the disk in and hit the Setup.exe
This will repair your system without affecting your programs or personal stuff.
While I've never used a WPE disk, when you boot up with a system repair disk to navigate to the command prompt to carry out any repairs, you are booted outside of Windows so at the cmd prompt to find where to execute any repairs, you need to enter the cmd
bcdedit |find "osdevice" and whichever partition letter that returns is where Windows sees the volume as installed, as it isn't always C: