GUI Opening Procedure Help

I'm trying to get a GUI to open when a player sneaks and right-clicks at the same time but am having a lot of difficulty doing so. I don't see anything inside the list of procedures that says, "Open GUI", or whatever it'd be called. It's important to me that the GUI of the block only opens with sneak + right-click, not just a simple right-click.

For whatever reason, MCreator doesn't let me post screenshots in here, so I'll do my best to describe it.
My current code is an Event trigger for when the block is right clicked, below it is an if statement, and attached to the "if" is a block of code that's titled "is Event/target entity sneaking" Does anyone know where a procedure for opening a GUI would be?

Thanks!