To change the orientation of the whole document, select Layout > Orientation. Choose Portrait or Landscape. Change part of a document to landscape Select the content that you want on a landscape page.
ArcGIS Pro – Layouts Changing from Portrait to Landscape and vice verse
Portrait and Landscape Layout in ArcMap
ArcGIS Create A Map Layout.
Frequently Asked Questions
How do I reset the layout view in Arcgis?
You can reset your data frame rules by clicking Clear All on the Apply Data Frame Rules dialog box. This clears any preconfigured rules set within the Apply Data Frame Rules and Data Frame Rules dialog boxes. This is useful when creating and saving multiple data frame rules in a sequence. Switch to layout view.