Converting datetime format in pandas for timeseries analysis

Question

I have time-series data. However, the date format is %dd.%mm.%yyy ( i.e : 01.01.2020). ( pandas data type is object).
I want to do time series analysis. how can I change the format so that I can do time series analysis?

I have tried the following code.

df["booking_day_new"] = pd.to_datetime(df.booking_day.dt.strftime('%d-%m-%Y'))

also

df['booking_day'] = df['booking_day'].dt.strftime('%d-%m-%Y')