Passing data between viewcontrollers

Hi

Total newbie here. Please forgive me if a) the question is so low-level that it should’t even be here, and b) if I’m inadvertently not supplying enough data to answer it.

I’m working in Xcode (Swift 5) trying to pass the values of three variables - property1, property2 and property3 - from a view controller called “SelectionViewController” with a storyboard ID “selectionVc”
to another view controller called “viewController” with a storyboard ID “mainVc”. I’m selecting the values of each of the variables via pickerview in the SelectionViewController.

I have an @IBAction set up in SelectionViewController that switches to mainVc and I have tried to pass the values across by attempting to replicate solutions offered on the Internet, but no joy.
How should I approach this?

thanks for anything that might get me closer.