How managers release me to rmg. What happens in background. Would I moved to rmg immediately or does it take time. Would manager provide me a notice or should I ask him?

If it is showing unallocated then you should

If your release date has been finalised between you and your manager over mail,then the next steps are to be done by the manager only. Your project allocation would be reduced/increased upto your release date. You would start getting calls from rmg and other projects around the last week of your allocation. You would be automatically under RMG once your allocation ends. If your release date has been finalised, make sure you have confirmation on official TCS mail from your manager.

No need to ask manager ur released automatically get email released to RMG on effective date u will move to RMG.