```
import pandas as pd
test_df =pd.DataFrame({"col1":[1,12,3,4],
            "col2":[3,14,5,6],
             "col3":[4,5,6,7]})

print(test_df)
   col1  col2  col3
0     1     3     4
1    12    14     5
2     3     5     6
3     4     6     7

def highlight(row):
    df1 = pd.DataFrame('', index=row.index, columns=row.columns)
    # set columns by condition
    df1.loc[row['col2'] == 5, 'col2'] = "AA"
    df1.loc[row['col3'] == 5, 'col3'] = "BB"

    return ret

df_output= test_df.apply(highlight, axis=1)

```

Error given above code: AttributeError: 'Series' object has no attribute 'columns' Request you please help me to correct highlight method code.