To do Return Shipments you need to have Logistics Account in atleast one of our Logistics Partners along with your Account's API Credentials.
If you have Logistics Account & API Credentials then you can easily connect your Logistics Account with REX for doing Return Shipments.

Logistics Integration Process :

1. Open REX
2. Go to Logistics Settings
3. Click on your Logistics Option
4. Click on Add Credential button
5. Add any Custom Account name & your API Credentials
6. Make sure the Test mode button is off, if you have Live API Credentials
7. Click on Save
8. Click on Activate to activate the Logistics

You can follow the same process to add Multiple Logistics Account if you have.