Both plays and formations can be flipped using the flip button  located under the play/formation diagram on their detail page:

Clicking this button will flip the play horizontally in the diagram so that it can be viewed and animated in both directions. For plays this is purely cosmetic but for formations it impacts which version of the formation will be used for sharing.

When you share a formation the version of the formation that’s used for the new play will be the one that’s currently displayed in the diagram. So, if you’re looking at a formation that’s strong right but you want to design a play that’s strong left simply flip the formation before you click the share button to create the new play.