An adder takes 3 input bits, A,B, and C-in. It generates 2 output bits, S and C-out.
What’s it even supposed to do?
I guess this is the solution you are after? I think it will help others if you name the bits in your starting position.
In your set-up, you only show two blue balls at the top. I assume though that three blue and three red balls are allowed. If not, then it’s back to the drawing table.