I’m not sure he could do an EO for that, or that if he could and did and someone still died, that he might be held liable legally for their death. I think you are asking him to endanger himself even more than he already has in service to this country.
Trump would not be prescribing treatment to anybody. He would simply give doctors across the country the right to do that themselves. He could sign an executive order allowing patients the right to request that it be used. The point is to remove the ridiculous roadblock that has resulted in more people dying than should have.