I believe that is an error in the help file. There is no global override that I can see that will beam eighths in 2s. This option is available, however, in the full version of Finale, just not in Print Music.

I assume you saw the way to break and join beams with the Speedy Entry Tool. This is your only option and sadly it's a lot of work. Why not consider upgrading to full Finale? You get a price break if you purchased Print Music.

You can also break beams with the simple entry tool. But as Bruce says, it's a pain if you have a whole score to do.