Looks like only latest 3 Simulator Images are available -9.7,9.6 & 9.5. NetApp site has been upgraded recently, so the old link now automatically re-directs to the new tools url, but I am not sure if it's possible to access old URL.
Anyway, any reason for Ontap 9.4 Simulator ? Are you trying to test any scenario specific to Ontap 9.4 ?
You can try this workaround:
1) Install 9.5 Simulator image.
2) Download 9.4 Production Image.
3) Get the 9.4 Image on the Simulator Node.
4) Follow the standard system node revert-to procedure to downgrade from 9.5 to 9.4.
Reverting an ONTAP cluster: (Obviously not all steps apply to Simulator, but the procedure works).