Hi Archana,
You can use transaction BD54 to create a logical system and use that within your partner profiles.
Usually, SAP systems are identified as <SID>CLNT<client>, but feel free to use something you like or perhaps you have to stick to some naming conventions.
For a SAP PO system you could use <SID>CLNT000 or <SID>CLNT001.
Kind regards,
Dimitri