Daniel,
I think you mean you set the wrong arrow style in one drawing?
Once you've change the arrow style in the preferences correctly, place another plant callout in the drawing. It will actually take on the newly set arrow, even with the old arrow style still in the drawing. Then use ACAD Match PRoperties (MA) to match the old ones.

If you mean something else, please attach a screenshot of an example of what you're trying to fix, or send in the file in our ticket system for me to look at.

-Amanda