How to Unregister 4D Client:

No matter how the client machines have been registered, you can unregister them for the current session using the UNREGISTER CLIENT command. When you use this command, the clients name will disappear from the user process group on the server machine as well as on the client. You can find more information regarding the UNREGISTER CLIENT command here:

https://www.4d.com/docs/CMU/CMU00649.HTM