Tap the Voice to Serif icon at the bottom of the screen to display the settings screen.
Tap the pen icon in the upper right corner, and a pen icon will appear in the upper right corner of the registered speech bubbles.
Tap the pen icon and an editing dialog appears.
After editing the text, tapping the "Decide" button will bring up a save confirmation dialog to complete the editing.
To cancel editing, tap the pen icon in the upper right corner again.