I'm new to goLang, In maps even though I can print the value, why I cannot change it?

Question

var sudoku = map[int][9]int{   // map of 9 x 9 
    0: {3, 0, 6, 5, 0, 8, 4, 0, 0},
    1: {5, 2, 0, 0, 0, 0, 0, 0, 0},
    2: {0, 8, 7, 0, 0, 0, 0, 3, 1},
    3: {0