The action he failed to take was mainly not letting the people know the possible seriousness of covid.When he clearly stated on the tape it was easily transmitted via respiratory means and 5 times more lethal than flu.
After that the action he failed to take was to initiate mitigation factors such as masks and distancing.
The answer to your question as to what could anyone do about a new virus that no one knows about is simple.
Initiate early aggressive widespread testing followed by masking and distancing.
These are certain conventions that hold for virus outbreaks that are well known.Other countries have utilized them and managed much better than we have.
They have not had near the medical damage or the economic damage we have had and continue to have.