The short answer is yes, just edit it and select it from the drop down box and hit submit again - see below why you probably couldn't do this when you submitted it. I think it is still an edit that does not require mod approval but I'm not 100% sure, so it might take your story offline for a short time. Add a note to the mods so we knit that's all you've changed just in case.
Currently only the author is able to add a story to their series - us mods only see a list of our own. Series that existed before the move only became available to you with an update last Friday. However, if it's like all of mine, the order will be all over the place. I've asked the development team a few questions to find out what the options might be to fix that.