Q.do I prune my crape myrtle and when
I live in Long Island and my crape myrtle is very tall. I would like to prune it. When do I do this and how do I do it? I don’t know how much to cut off and where on the tree. It is now November and all the leaves are gone.

Though pruning is not necessary for a Crepe Myrtle, but if you determine that your's need some clean up, prune while in dormancy.
Here is an article with more information.
https://www.gardeningknowhow.com/edible/fruits/date/date-palm-tree-care.htm