When you create an alternate layout this modal pops up allowing you to choose a page size with width and height dimensions. After you've selected "OK" how to you get back to this modal? When you go to File > Document Settings it only shows the settings for the main layout (frist layout created). How do you get to the doucment presets for an alternate layout?
You could use the Page tool.
In the Pages panel, highlight the master page used by the alternate layout you want to change. Choose the Page tool. Enter a new page size. Because you're applying this to the master page, it will apply to all the document pages based on it.
Thank you so much! This worked for me.