How to create custom app use rocket chat jar.file

I created a jar file via this link. I want to use rocket chat in my custom android app. I want to use java sdk but I know it was terminated in 2017. So I have to use Kotlin. I added the jar file to my project lib folder. There is no example of how to connect to Rocket Chat after this. Where can I find it? Help me.

i need example code… plz… Is this supported? TT