Hi Srini,
In the feeder system, you need to set the Delivery Type so that it transfers to GTS for Customs Management, but do not check the "before GR" box.
In the Foreign Trade & Customs tab of the Inbound Delivery header, you need to enter a Preliminary Document Type and Number, to represent the Movement Reference Number (MRN) of the Transit movement.
The Preliminary Document Type (typically 'T1') must be configured in the feeder system, and also mapped in GTS to determine Target Procedure '01' ("Transit"). Those GTS settings are at the top of the "Customs Management" > General Settings area.
Hope that helps.
Regards,
Dave