Arati, follow this note, it is exactly what you need:
1915825 - Transfer Posting reference to a Purchase Order in MIGO
Resolution
The business function 'LOG_MM_OM_1' must be activated in your system.
Also, the BADI MB_MIGO_SC_PO_TRANSFER must be activated into the system and then the option 'A08 Transfer Posting' and 'R01 Purchase Order' appears.
To activate the business function go to tcode SFW5 and mark the function LOG_MM_OM_1 and click on Activate Changes.
After that you can go to MIGO and check:
Regards,
Felipe