Would like to change the String Datatype to Date Datatype extracted from absWeek(),Week()...etc

Would like to change the String Datatype to Date Datatype extracted from absWeek(),Week()...etc

Hi Zoho,

As I need the sum of sales per week which has to be automatted every year weekly,I have extracted the Created data on  absWeek() ,As the data is changed to string.
I would like to change String format absWeek() data to Date format,So that I can use it, in charts to plot last 4 weeks Sale's.

When I try to change in table it gives error as Data Type set for the column is not compatible.

Please guide me to overcome the problem.

Thanks in Advance.