Convert page layout on all pages
This seems like such a simple thing, but even between many years of ID experience and every relevant page I can find on search, no answer has come up. (I have found or been reminded of how to adjust everything, but not make it apply to existing text frames.)
I have a document (actually, many of them) with 2-column layout. Partly to facilitate export to EPUB, I want to convert all pages to 1-column.
If there's a way to do this without selecting every text frame and changing the column setting, I haven't been able to find it. (Nothing I can find in the Pages panel, Layout menu or Document Setup pane will adjust the existing text frames.)
So, what am I missing here?

