2d arrays inside 2d arrays in c++

I'm coding an ultimate tic-tac-toe* game in c++ (Microsoft Visual Studio), but I've encountered a problem.
To make it work, I've made nine 2d string arrays, one for each square in the larger grid; and one 2d string array for the large board. My plan is to make, for example board[1][3] = botLeftGrid; but you can't set places in an array to entire arrays in c++. Am I doing this wrong, or is it just not possible to do this this way? Or would it be easiest just to make a function that returns a string value based on the inputs?

*All you need to understand is that there are tic-tac-toe grids in each of the nine squares of a larger tic-tac-toe grid.

 

thanks