If you use "Audit Accidentals" from the "Tools" menu, that should do the trick. It's in the Help, but only if you can find it! It says:

"This command can be used to remove any unnecessary accidentals assigned to notes in the active staff. It compares all notes with the running key signature, and if the accidental it contains matches the running signature, then the accidental is removed.
Copyright ® 1998 by NoteWorthy ArtWare, Inc."

Steve