E0023: Unknown Enum Variant

You referenced a variant that doesn't exist on the enum.

Example

enum Color {
    Red,
    Green,
    Blue,
}

fn main() {
    let c = Color::Yellow;  // Error: enum `Color` has no variant named `Yellow`
}

How to fix

Use a variant that exists on the enum:

enum Color {
    Red,
    Green,
    Blue,
}

fn main() {
    let c = Color::Red;  // OK
}

Or add the variant to the enum definition if needed.