You can flip the location of a target shape on the base object using the Shape Editor. The flip moves the target shape according to the axis that you choose, resulting in a completely reversed shape. Flipping is similar to scaling an object with a negative value (-1) in either X, Y or Z, but only the selected target shapes are affected.
No additional target shape is created when flipping - that is, you're flipping the actual target shape, not creating a flipped version of it. If you want to do that, first duplicate the target shape (see Duplicate target shapes), and then flip it.
If the target shape has in-between shapes, they're also flipped.
Watch this video or follow the steps below to flip target shapes.
To flip a target shape
For a group of target shapes, right-click the group name and choose Flip Group Members.
The target shape is flipped on the base object according to the current options.
Select the symmetry axis to be used for flipping the target shape.
If there is no symmetry seam already defined for the object, you are prompted to select an edge (Edge mode is enabled) as the flip axis.
Store topological symmetry seam edges: Available only if you select Topology. This option stores the last-defined edge as the symmetry seam used for this blend shape deformer, and is shared with the Mirror Target command. If you flip a target shape that belongs to another blend shape deformer, you are prompted to select an edge again.