Turn off Media?

Hello, 

I'm newer to triggers and I've built a simple trigger/layer interaction, where on the first main layer there is media leading to the first layer where it plays additional media and goes back to the main base layer and then again plays that media again. 

Is there a way to turn it off after it's played the first time? Because I want the learner to go to additional layers and it seems when they click on those layers the base layer media overlaps and plays. 

Appreciate any help

Thank you