I want to change string datas in dataframe to datetime data
but it's not working
for example I have dataframe data here

```
TotTime
D1 12:24:13.88
D1 12:24:14.88
D1 12:24:15.88
D1 12:24:16.88
D1 12:24:17.88

```

and I want to change this data in date time to caculate
How can I?

I tried like below

```
df.StepTime = pd.to_datetime(df.StepTime)

dfn['totTime'] = dfn.totTime.apply(lambda totTime: datetime.strptime(totTime, 'D%d %H:%M:%S'))

dfn['totTime'] = dfn.totTime.apply(lambda totTime: parse(totTime))

```

but it was not working