Shift row in 2D Vector

I have a Vector like below:

vector<vector<double>> A;

And have values Like this:

1,2,3
3,4,5
5,6,7
8,9,6

I want to shift row down with step 3 and then become below:

3,4,5
5,6,7
8,9,6
1,2,3

How can I do this?