This article provides answers for InVision V7. Not sure which version you're using? Find out now.
When viewing the public share link for an InVision V7 prototype, you can switch to any screen via the thumbnail tray.
To open the thumbnail tray, navigate to the bottom toolbar and click the current screen name. You can then search for and select any available screen. To view the screens in a grid view, click the expand icon () next to the search field.
If you don't have the option to show or hide this bottom toolbar, it's likely that the setting Hide InVision UI is enabled. Once that setting is turned off, the toolbar should appear.