To mount a .WIM file in DISM you can use the following command
Mount-WindowsImage -ImagePath "c:\yourpath\Install.wim" -Index 2 -Path "c:\Mounted_image"
Index number depends on your WIM but in most cases the standard is 2
I recently stumbled into an issue while removing apps from a windows 10 install.wim where i couldn’t run the script due to the image already being mounted. To get around this issue you need to unmount the image in DISM using the following commands.
dism /Unmount-Wim /Mountdir:C:\examplepath /commit
If you do not know the mount directory you can find it and view all mounted images by using the following command