As of Final Draft Go 7.2.0, released 09/04/24, you can swipe left and right to cycle through elements! This will work both on lines with existing text, and empty lines. The examples below are for iPad, but they will work the same for iPhone.
Place your cursor on an empty line, and the Scene Heading element will be highlighted above the keyboard:
Swipe to the right on your screen, and the element will switch to Action:
You can swipe right or left to cycle through the elements as you need.
You can also do this to change existing Elements. For example, this Dialogue element:
Changes to Action when swiped to the left three times:
This can also be used to change Outline element levels. The Outline Elements will be within their levels of selection, so if you select Summary:
and then swipe right again, it will cycle back to Outline 1 instead of Scene Heading: