Reg: New installation number

Hi Gurus,

We have to add new installation number to one S-user. Because he is unable to sent a customer message in SAP market place. Right now user name is assigned to another installation number. I am trying to change that but there i didnt found the entire installation numbers. Please let me know how to create new installation number or how to add?

Thnx in advance.

with regards

Harish