I had this last week after 2 abortive attempst to resolve, I started a "new" itmp by hitting pubish in iBA
First copy your books vendor ID from iTunes Connect and when iTunes Producer starts.. insert your vendor ID.
Fill in all the details as you would a new book, Description can be copied from iTC if you dont have it elsewhere.
Producer will ask if the book is the original or an update - if you have changed the book.. its an update 1.1.
You need your cover and screenshot images AND.. unless it picked me out for special treatment.. you need a preview of upto 15 pages. I only do free books and never had this thrust at me before - but I could not get the book delivered till I made a preview, simply by duplicating the book and adding XXX-Preview to the iBA name and chopping the book up until I had the maximum 15 pages. after that it delivered OK.
In iTC you will get a new orange dot with 1.1 in Review. You book will not be updated till its reviewed and approved.
BTW, you need to update iTunes Producer.
It seems once again Apple change the process routine and say nothing