How do I redefine chord variations when editing songbook

How do I redefine a chord variation when I'm editing a song in songbook? For instance, if my chord diagram shows a different chord variation than the one I want to use, how do I change it?  I read somewhere to click the chord grids to select another chord variation, and that the redefined chords will automatically be saved in your songbook, but I must be doing something wrong because the new chord shape is not being saved to my edited song.
Sid