Current thinking is that Ice-Water enemas do bring a fever down, but are used ONLY as a last-resort for severe Hyperthermia.
There is some evidence that a typical enema, usually of cooler, but NOT cold, water, or something like flavorless pedialite (preventing electrolyte problems), will cause a fairly substantial reduction in fever in cases where it isn’t due to a severe pathology (like Hepatitis, Systemic Bacterial infection, Viral Infections, etc).
But like every other possible application, the association with “Medical Quackery” has made more mainstream Medical Science reluctant to test such things.
Odds are likely that the ice-water enema as a last resort is sound (supported by evidence). And possibly that an enema will prompt a more rapid natural resolution to some illnesses, such as basic headaches or fevers not cause by something requiring a substantial course of medication to resolve the primary cause.
But the storm of biases surrounding the subject prevents any objective testing.
Edit:
Google “Ice water enemas as last resort for Hyperthermia.” It will take you to NIH and CDC sources about how this has been SOP for a long while.