how to iterate over certain rows of a certain column an update their value. by applying condition
You can use df.loc to make the selection and then set the values. Take a look at this example and modify according to your dataset.

In [1]: import pandas as pd

In [2]: df = pd.DataFrame({'a':[1,2,3], 'b':[0.1,0.3,0.9], 'c':[4,5,6]})

In [3]: df
Out[3]: 
   a    b  c
0  1  0.1  4
1  2  0.3  5
2  3  0.9  6

In [4]: df.loc[df['b'] &lt; 0.5, ['a', 'c']] += 20

In [5]: df
Out[5]: 
    a    b   c
0  21  0.1  24
1  22  0.3  25
2   3  0.9   6


Also, in future try to provide a sample from your dataset as a table of values and not an image so that it becomes easier to reproduce an example.