You can access the zoom/scroll settings from the configuration cogwheel on the bottom right toolbar of desktop prototypes:
Here's a little more information on how the zoom/scroll feature behaves:
This leaves your screen as-is.
Hide Horizontal Overflow:
This keeps wide screens from being able to scroll left and right when they expand past your browser view
Scale Down to Browser Width:
This scales your design down to the width of your browser window if it's smaller than the design. The scaling is active and won't require a browser refresh.