column += increase

This actually only increases the iterator. You Actually want to increase the element from your matrix, which would look something like this :

def change_value(my_matrix: list, increase: int):
    for row in my_matrix:
        for column in row:
            my_matrix(row,column) += increase
    return my_matrix

matrix = [[1,2,3],[4,5,6],[7,8,9]]
change_value(matrix, 3)