That warning means that in the next version of the engine, they will be getting rid of that node. Everything should still work with a deprecated node, but to fix it, you can simply place the new node, which should have a similar name (Set Input Mode Game and UI).What is it with importing this that you are having trouble with?
The demo project I have included is just an example, and one of many ways to use the plugin in your project. You can setup the Easy Input Remapping nodes with your UI however you’d like. In my demo project, I’ve shown how you can setup an interface to listen for new button presses in order to remap your keys, so you can ignore all of that if you have your own interface made.