The Symmetry command allows you to make symmetrical components when editing so that you can have more control over your shape. Keep edges and faces on each side symmetrical to simplify the editing process.
- On the ribbon, click 3d Model tab
Freeform panel Symmetry 
. If necessary, click the drop-down menu to access Symmetry. - Select a face on the master side and another face on the mirror side.
- Click OK.
Once created Freeform edit tools maintain symmetry so changes on one side of symmetry are reflected on the other side of the symmetry zone.