Touch and hold on the first character name until the menu bar appears**:
Touch Create Dual Dialogue...
...and the paragraphs will be positioned side by side:
To undo dual dialogue, touch and hold in the dual dialogue until the menu bar appears. Touch Un-Dual Dialogue and the paragraphs will be positioned vertically again.
** If you're using FD Go on an iPhone in Portrait mode, you may have to touch the arrow on the right side of the menu to show the command to create dual dialogue: