Given x and y from an array of tuples change the value in a Matrix

So I have this Array of Tuples:
let pos = Array.init 2 (fun _ -> Scanf.scanf "%d %d " (fun a b -> a,b))
And a Matrix:
let board = Array.make_matrix 4 4 0
I would like to, given the position x,y from each tuple, change the matrix.(x).(y) value to 1

Array.iter (fun (x,y) -> board.(x).(y) <- 1) pos