Hello Abhinash,
The "Start Retrofit" Action would be available even after the Retrofit has been completed for the Change document. The action is available in the dropdown based on the Schedule conditions for the Action.
The "Start Retrofit" action would still be required to view the completed retrofits for the change document.
What is the status of the Retrofit against the Specific Source Transport Request/s? Is it showing as Retrofitted or not?
Regards,
Kathir