How to parse data from one field using data source

I am using an Excel file as datasource and have one field in the file marked "DOB" in the format YYYYMMDD.  In the API request I need to parse out the dates from the field separately?

What would be the best method in doing this for the request - for example mapping the YYYY information into a request field, the MM information to a request field, and the DD information to a request field?

Thanks