Evolution is a theory. A theory. You don’t “discover” a theory, you create it.
Now if by “evolution” you mean micro-evolution (development of a species within itself), a scientific reality which is observable and repeatable, then it would be accurate to say that it was “discovered.” But then it wasn’t Darwin who discovered micro-evolution.
But if by “evolution” you mean macro-evolution (the development of one species into another species), you are dealing with a theory that has never been observed, cannot be repeated, and which is questioned by a significant portion of the scientific community.
Darwin can be credited with “discovering” some things, but evolution is not one of them.