When you press the enter key in a terminal program it sends normally the carriage return and line feed character. You have to do the same in your LabVIEW strings by adding those characters to the end of a command string.
Enable backslash code in the right click menu of your string control or constant and add \r\n to the end of your command string.
Enable backslash code in the right click menu of your string control or constant and add \r\n to the end of your command string.