Squeing belt

don’t have any belt dressing. can I use silicone spray on a squeing alternator belt. I hear silicone is good for rubber parts.

No. Silicone spray will allow the belt to slip. If the belt is squealing you most likely need a new belt or a pulley bearing is on it’s way out.

Yosemite

thanks Yosemite has a new belt on it just replace a bad alternator.

You could loosen the belt and while loose, try spinning each pulley. Wiggle them and also pull it in and out, to see is one has play in it.
Any suspect pulley should be replaced, because the squealing you hear is the bad pulley wearing the new belt out prematurely.
Be sure to also check the idler pulley and the tensioner pulley. Many people miss those.
A too loose tensioner (weak spring) can also cause a squeal.

Also check that each of the pulleys grooves are clean.

Yosemite