When you create a symmetrical copy of a piece, the pieces are linked by that symmetry. If you decide you no longer want the pieces to be symmetrical, you can cancel the symmetry.
To cancel the symmetry:
On the Main toolbar, click Select.
On the Horizontal contextual menu, ensure Pieces is selected.
In the 2D window, click the piece that was created as a symmetrical copy of the original piece. Do not click the original piece.
For example, in the following image, piece 71 is the original piece. A symmetrical copy was created, forming piece 72. To cancel the symmetry, you click on piece 72.
Go to the Context view, in the Actions section.
Click Cancel. The symmetry is canceled.