How to call back a function within a custom ViewRenderer?

I created a custom renderer (called HybridWebViewRenderer) subclassed from the ViewRenderer class.

From the PCL, I have a ContentPage with a button and a HybridWebView.

From the PCL, I want to be able to call a function thats in the HybridWebViewRenderer class so that I can do some work with the webview.

How can I call the function?