If you had used our 'Search' function you would have seen your question asked before. "Take a moment and review information on the FAQ link on your Dashboard. In the FAQ there is this: "My book was previously accepted to the Premium Catalog, and then I made a change and it's asking me to resubmit it for consideration. Why? For any change to your book other than price, your book must be manually reviewed again before the new changes will ship to our retail partners.This is to ensure the changed book and its associated metadata still meet the requirements of the Premium Catalog. During the time that your book's status reads, "Pending Review," the previously approved version will continue to ship."
It's good that you posted here before contacting Smashwords. Every author should read or re-read the FAQ's and other supporting documentation on Smashwords before submitting a Support request to Smashwords.