ITMS-90809: Deprecated API Usage - UIWebView

I have followed all instructions on https://ionicframework.com/blog/understanding-itms-90809-uiwebview-api-deprecation/ but I still see reference to UIWebView after I build. Also, the instruction says

add <preference name="WKWebViewOnly" value="true" /> to your config.xml

But doesn’t really say where to add it. in the Platform section or Widget. am literally stack right now