I'm making an app on Android but want to know if there's any way to easily make it compatible with iOS.

The simple answer is No. You will need to recreate your app using the tools/language required to develop any iOS app (Mac, Xcode, Swift/Object-C) . However, there are some tools, like Xamarin, Reach Native, and others, that let you write an app once and run it in both; Androind and IOS. But you need to use that from the start.