In general: try tapping the dots at the top of the app, or tapping the app's icon in the dock. For Mail specifically: there's an icon in the lower-right of the

In general: try tapping the dots at the top of the app, or tapping the app's icon in the dock. For Mail specifically: there's an icon in the lower-right of the sidebar that looks like two squares, one on top of the other- try giving tapping that.