Can I assign and unassign existing transports?

Yes, but the existing SAP Transport must be Modifiable:

• You can use the Manual Assignment section to either add a reference to an external ID or assign an existing SAP transport.
  
  
• From the Transports List, it is also possible to unassign an SAP transport that has been linked to a Change.

If you notice the app returns a success code after assignment but the Transport is absent from the list, this generally means other backend fields may not be valid.

Navigate to SE01 to display your Transport and verify you can edit the details without triggering an error.

-- We do NOT recommend to perform the below approach as it may corrupt your system! Always seek advice from your team first. --

In the event where the transport is already Released, you may still be able to do so by following these steps:

• Start transaction SE38 in the backend.
  
  
• Execute program RDDIT076.
  
  
• Enter the Transport ID and confirm.
  
  
• Double-click the Transport entry.
  
  
• Go to Edit mode.
  
  
• Change the Status from value R to D.
  
  
• Save and unassign the Transport in Freshservice.
  
  
• Go back to the Transport entry in the backend.
  
  
• Change the status from value D to R.