Try a downward 3 finger swipe to expose the tool bar where you can tap to get options that include selecting layouts.
But the settings/scripting that pull up the correct layout should be figured out and corrected. A startup script that checks to see if the file was opened by FileMaker Go is usually used for this purpose.
For FMGO I highly recommend creating a popover with your navigation options. Place the popover button in the same location on each layout if possible. This will allow your users to consistently know where to go to navigate.