Value used multiple times

Hi

Mine is an Idoc to File scenario on PI 7.1. I have a particular field ORGID used many times in the target for different fields.

The mapping logic is like this

Target            Source

Start Date  -  E1EDK03 segment field DATUM with qualifier 10

End date  - E1EDK03 segment field DATUM with qualifier 15

I have imported the IDoc to mapping. Howeve when I do field mapping, I am not able to incorporate this logic. How do I go about this?