There are a couple of ways to accomplish this:

Method 1

On UNIX/Linux clients, the guid is stored in the /opt/altiris/notification/nsagent/etc/host.GUID file.

1. Delete the Linux computer record from the Notification Server console.
2. Stop the Symantec Management Agent with command: aex-helper stop
3. Delete the host.GUID file on the client
4. Start the Symantec Manangement Agent with command: aex-helper start
5. Resend basic inventory with command: aex-sendbasicinv

Method 2

Uninstall and reinstall the agent on the client computer.  

If either step does not work, select and delete the corresponding entry in the resourcekey table for the erroneous GUID and repeat the process.