[Python] replace first row value with last row value

I'm trying to take the value from the last row of a df col and replace it with the first value. I'm returning a value error.

import pandas as pd
df = pd.DataFrame({'name': ['tom','jon','sam','jane','bob'],
'age': [24,25,18,26,17],
'Notification': [np.nan,'2025-01-03 14:19:35','2025-01-03 14:19:39','2025-01-03 14:19:41','2025-01-03 14:19:54'],
'sex':['male','male','male','female','male']})

df_test = df.copy()

df_test['Notification'] = pd.to_datetime(df_test['Notification'])

df_test['Notification'].iloc[0] = df_test['Notification'].tail(1)


Error:

ValueError: Could not convert object to NumPy datetime

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