Hello,
In your case, Insert the username and Password of computer and under Domain type "Workgroup"
Check these Articles:
How to deploy clients in Symantec Endpoint Protection 12.1
http://www.symantec.com/docs/TECH164327
Steps to prepare computers to install Symantec Endpoint Protection 12.1 client
http://www.symantec.com/docs/TECH163112
When installing the Symantec Endpoint Protection client via the Symantec Endpoint Protection Manager in a Workgroup environment (not on a Domain), we will require the following prerequisites:
- Disable Simple File Sharing on all target clients.
- Disable the Windows firewall, or enable communication on TCP ports 139 and 445 and UDP ports 137 and 138.
- File and Printer Sharing for Microsoft Networks is enabled.
- The C$ and Admin$ shares on the target clients are accessible from the Manager system.
- There is an password-protected Administrator account common to all target systems that are being simultaneously deployed to.
Reference: http://www.symantec.com/docs/TECH105662
Hope that helps!!