Can I submit work that has already been published?
If you are planning to revise an already published piece with the goal of publishing it as a revised reprint, you may post it in the queues.
However, the queues are not a place for self-promotion, and you should not post a story as an ad for your published or forthcoming work. This is not fair to the critiquer, who spends time and effort on a critique that will go wasted, and it is not fair to other CC-ers, as it takes up a story slot that could be put to real use.