Mainframe Automation - Press Left control key

[ppr (Peter Preuss)]

have a look here:

@tclukay

When this happens, we used to use the Terminal Send Control Key to send the “Reset” key to the session to unlock the keyboard. This no longer works. The only way we have been able to do this is to attach to the emulation window and send a left-control key press to the window.

taken from: 5250 Terminal Connections: Resetting locked keyboard?

UPD1-
Also scroll down when the RESET key is mentioned