Symmetry Constraint in Size Optimization

Hello,

I am working on design optimization of an aircraft component. I have obtained the shape of the required object using a topology optimization and am interested in refining the thickness of the part using a Size Optimization.

However, I am unable to find an option to create a plane of symmetry in the DESVAR card or any other location. The results obtained from the optimization show a density distribution that is not symmetric either.  Is there anyway to do this?

Please let me know.

Thank you!