Adjust margins in existing book files

Using macbookair OS 14.6 and ID 20.0.1

I have already laid out a novel (600 pages) that is broken into 6 separate indd files that are linked with an indb file as a book. All the pages have text boxes that fill the page and flow from one to the next.

Now I find out that I need to shift all the margins 1/8" toward the outside to make for a deeper gutter. The text box width will stay the same — just shift over. If I just set new margins in File > Document setup, the text boxes will remain in their original position. Is it possible to somehow have the text boxes automatically move to fit the new margins?