Hi Naveen,
Reading the partner GUID is a two step process:
1. First read the GUID of the BT.
2. Pass it to FM CRM_ORDER_READ and get the partner details from the exporting parameter ET_PARTNER. Read the partner with appropriate partner function.
Once you get the partner number, either use FM or query BUT000 to read the partner guid for the partner.
Then follow the steps i mentioned earlier.
Hope it helps.
Regards,