Hello,
If we are requesting the part through a claim, follow the procedure outlined in Memo1939.
https://quickserve.cummins.com/qs3/pubsys2/xml/en/memo/2019/m1939.html
If you are just sending back cores, please reach out to your Regional Core Management Team as found in the Dealer Support Contact Manual linked below:
https://quickserve.cummins.com/protected/files/qsol/cms/dealersupportcontactmanual.pdf
I hope this helps.