I have been programming a Python desktop app in Python 3.7 with tkinter. Many of my friends have said using it as an mobile application will get more users. I have been working with sklearn and different modules in Python to run along side the GUI. Is it possible to call that script in Kotlin?
Yes it is possible.
Python has REPL, it's own interactive interpreter and as it turns out Kotlin has a REPL as well. You'll still have to do research and find the interfaces to use with your front end.
NOTE: In Intellij Idea Kotlin has REPL. I'm afraid I don't know if it's the same with other IDEs. 
If it's only for Android, you can use QPython.
QPython is a script engine which runs Python programs on android devices.
Is there a way to call Python script inside of a Kotlin project?