how do you set a timing belt for a 2003 cadillac cts 3.2l v6 ?
You need a shop manual for specific instructions. Check your local library. Some have a collection of auto repair manuals.
Why are you under the impression that your Cadillac has a timing belt? And, what do you mean by “setting” the timing belt?
Is replacement of the timing belt mentioned in your Maintenance Schedule at all? If not, then you do not have a timing belt, and instead you have a timing chain.