Unable to modify column

Hi Everyone

I'm still a beginner in Power Bi. I just created my profile in the Power Bi community.

I am stuck in Power query modification. 

As you can see in the image, I want to use this Date (split from text) in the same column or a new column but I'm unable to do so. I can use replace function by copying the Date and replace with a null but this copied value will be static whenever the data gets refreshed as I'm using Excel from Sharepoint location as Dataset.

Appreciate it if you guys can suggest how to do it.

Thank You.