No.
Just, no.
That's not how it works. That's not how any of this works.
I don't know whether powdered rhino horn works for COVID-19. Indeed, I am unaware of any testing of this hypothetical cure. Would you honestly say that it has a 50:50 chance of being effective?
So long as I am not removing other more reasonable opportunities from my choices by focusing on elderberry and not other reasonable choices, I am only adding to the probability of my successfully fighting it off faster. So if I get it and hospital beds are full and no other treatment options, I will take it and cross my fingers.
It probably won't do you any harm.
It also probably won't do you any good; But if you can afford it, and don't eschew other options because of your confidence in it, it's likely harmless.
It's assuredly not got a 50:50 chance of being effective, regardless of your lack of knowledge.