Im unable to backtrack

#1

My code is :- https://ide.codingblocks.com/s/379244
code is running good but on last step i’m unable to backtrack , can you please help me out .

#2

refer to this to understand :

    for (int i = 1; i <= 9; i++) {

                if (isItSafe(board, row, col, i)) {

                    board[row][col] = i;

                    boolean res = Sudoku(board, row, col + 1);

                    if (res)

                        return true;

                    board[row][col] = 0;

                }
        }