/Set-TargetPath: Sets the target path of the Windows PE image. The target path represents a path to the root of the Windows ...

/Set-TargetPath:

  Sets the target path of the Windows PE image. The target path represents a
  path to the root of the Windows PE image at boot time. A valid path is an
  absolute path that begins with a drive letter C-Z, contains no empty path
  elements ('\'), and must exist when the Windows PE image is booted.

  Example:
    DISM.exe /Image:C:\test\offline /Set-TargetPath:C:\test\image