Before you start hunting around, check the Recycle Bin! You may be surprised to see the DLL file there.

If you no longer have the .dll file, then you can search for it on the Internet and download it. Be sure to download only from reliable sources.

If you have made backup files of your system, you can try and restore the .dll file from it.

If you cannot find the file you need, you can try to repair the Windows installation and reinstall the missing .dll file.