I have created two books in Pressbook.
I wanted to combine these two book into a single book.
What I did,
I cloned the first book, and imported the second book, but while importing the book the chapters gets mixed up with the first book.
How do I import the second book that precedes the last chapter of the first book.
Or any other idea, how I can combine two books that precedes one after the other.
Hi @johnpeterm did you try importing from HTML, choosing import from URL and entering the URL of the desired book(s)? 
If you do this, it should let you choose the chapters you want to include from the other Pressbooks titles in question. I believe they’ll generally be included in the book in order of import, but can then be moved/rearranged using the organize tools.
Thank you @SteelWagstaff this method has worked and it helped save time.