Ok, now we need some clarification. CoachPaul is correct that the throwing arm will pronate on its own after ball release - regardless of which pitch is thrown. There’s nothing to think about to make that happen. However, there are some pitches (e.g. sinker and circle change) that are thrown with some pronation prior to ball release. These do require a conscious attempt to make that happen. Again, I prefer the focus to be on the hand or the spin you wish to impart on the ball.
Two things to watch out for:
(1) Don’t alter your posture to try to pronate beyond what your flexibility allows.
(2) Don’t allow your arm to sweep across in front of you as a result of your attempt to pronate. Make sure your arm throws through to your target.