Create SCM user as a Business partner

Hello,

I am looking at txn BP in SNC. My intention is to create an existing SCM user as person Business Partner. I don't see that option in txn BP but when I go to txn /n/SCA/USRPRTASSIGN I get the drop down option for all users in the system. I also get a message here which says 'This Is an Unsupported Test Transaction -  - Use Transaction BP'. But in BP I don't see an option for finding the system users.

Anything I am missing, please?

Thanks,

Subash