Hi, Dikkieduk
Look at Config, "System Hotkeys", Enter Trigger#, Then OemCode for "Start", Then in Ports & Pins, Inputs, Trigger# set to port and pin.
You could use Brain's, Operator, "Brain Editor" to do it, Configure an input in Ports & Pins, Input # to your external button.
Then Brain Editor, Look at the video's on Brain's Above under "Tutorials".
Describe your setup a little more, Well help if needed.
Many ways to do it, Let US now.
Thanks, Chip