How do I add the 'green arrow' on any condition?

Hello, I have a simple question. How do I add the green arrow on a condition (which will make the event trigger only once)?

Thanks all,

guannstart (Fnord)

You can use the "System:Trigger once while true" action. This is separate from the "green arrow".

Yeah, but, what if I wanted to use the green arrow, instead of the "Trigger once while true"? How would I do that?

You can't make something a trigger - it either is or it isn't. https://www.scirra.com/manual/75/how-events-work