Assuming that Txn_Date is a string, you can do:
df3 = df3["Txn_Date"].apply(lambda x: datetime.datetime(int(x[:4]), int(x[-2:])+1, 1))
What's happening here:
we take all values in the column and apply the following transformation to each value,
the first 4 characters are used as year, and last two characters are used as month and a fixed value of ...
It is common for data to change over time. One common name is for this phenomena is dataset shift.
There are two steps when dataset shift is possible: detect and update.
Detection can be done manually or automatically. A person can inspect the new data and decide if a new topic is present. The process of detecting a new target can be also be automated. ...