Any way to get the long α diacritic on Classical Greek Keyboard?

ie the line that goes over the alpha…

I’m using Gentium Plus on MAC OS 12.6 on 2021 Macbook Pro 2021 M1

Thanks — JM

Please refer to the keyboard’s help page at Greek Classical Typing Chart.

I just looked through the documentation. It looks like the combination would be:
a_
or
a [shift-hyphen].
the underscore/hyphen key should be the one to the right of the 0.