I have a UWP application and I want it to be able to run into Android and also IOS using Xamarin.forms. Is there anyway to port it and run it on both of them?
Short answer: no.
Long answer: Xamarin Forms is "Xaml" too, but works on top of a completly different framework.
If you have used a good architecture, you can use all your viewmodels (or whatever your ui logic is called) and just put a Xamarin.Forms UI on top of that. With a little luck, you can reuse a lot of the structure from your existing xaml, but as most names are different, it is almost a complete rewrite. Or you could put a native UI with Xamarin.Plattform UI on top of your code.
So if you want to go cross platt form, you have to add at least one completely new UI.