FDMEE adding Three source account to one Target Account.

I need to add up to 3 source accounts to one target account in a file-based integration where the source is File and the target is the EPBCS application. I tried using Explicit mapping and IN Mapping in FDMEE, but it’s not working. I even tried using the “Add Data” option in the Export Mode while executing the integration, even though that is not working. Can someone help me with how to achieve this?

Example:

Source Account:

AC_101 = 100

AC_102= 200

AC_103= 300

Target Account:

Basic Salary = 600