According to [this page][1], `Y` would be Button 4.

> Stick 1 = left analog stick
>
>Stick 2 = right analog stick
>
>POV = dpad
>
>Button 1 = A
>
>Button 2 = B
>
>Button 3 = X
>
>Button 4 = Y
>
>Button 5 = LB
>
>Button 6 = RB
>
>Button 7 = back
>
>Button 8 = start
>
>Button 9 = left analog stick center pushed in
>
>Button 10 = right analog stick center pushed in
>
>Button 11 = left trigger
>
>Button 12 = right trigger
>
>Button 13 = X silver guide button


  [1]: https://joytokey.net/en/posts/button-mapping-for-xbox-controller/