Python Help me fix this code

[DisguisedEagle]

def solve_board(board):
    for i in range(9):
        for j in range(9):
            if board[i][j] == '0':
                for k in range(1, 10):
                    if not check_number(board, k, i, j):
                        board[i][j] = str(k)
                        if solve_board(board):
                            return True
                        else:
                            board[i][j] == '0'
                return False
    return True

I am making a sudoku solver, I saw this code but it doesn't seem to work for me. It fills my matrix only with one's. I can see the problem but I need help.