You can present your case at anytime within Engage. To do this, click on Present in the top right corner:

A live and interactive presentation will appear:

When in present mode, navigation buttons will appear at the bottom of the screen - this includes moving forwards and backwards between slides, as well as zooming in and out:

To restore the view to fit the screen, you just need to press on the zoom percentage button:

To exit present mode, an X button will appear at the top of the screen, you can press Esc on your keyboard or press Exit in the navigation button.