How to change the royal piece.

Does anyone know how to change the royal piece in 4pc when your in the custom starting position settings?

I don't even understand your question.. I'm sorrryy

Do you mean you want to change the order of the back rank pieces in a custom match?

You mean like you Have to checkmate the knight instead of the king? As far as I know, you cannot, but you can otb if you want to just play it with friends.