When you run the session, the Integration Service looks in the directory you specify as the Runtime Location to find the library (DLL) you built in Step 4. The default value of the Runtime Location property in the session properties is $PMExtProcDir.
To run a session:
In the Workflow Manager, create a workflow.
Create a session for this mapping in the workflow.
Alternatively, you can create a re-usable session in the Task Developer and use it in the workflow.
Copy the library (DLL) to the Runtime Location directory.