TCP string echo

Hi all
i’m new to openHAB, after i got a TCP client to connect
it’s send a string to the server
the Item used is:
String sValue {tcp="<[192.168.1.21::'REGEX((.))’]"}
i need help woth the next issues:
how can i echo the string back to the client
how to define an On \ Off commands

Thanks.

The syntax is documented here:

thanks