Hello Marcel,
As you have extracted the data, I assume you would have some scheduled jobs to extract these data in SAP. Now in order to import these data in Ariba, you should place these files in outgoing/outbound folder in ITK (the folder in which you have extracted ITK) from the data transfer tool will pick up these files/data and load into Ariba. Indeed for loading these data into Ariba you can again have the scheduled jobs or can configure the corresponding events/tasks.
Hope that helps.
Thanks,
Sandeep Jain